What is the BUN/Creatinine ratio. How does it reflect kidney function. What causes high or low BUN/Creatinine levels. What is the normal range for BUN/Creatinine ratio. How can you improve your BUN/Creatinine ratio.

What is the BUN/Creatinine Ratio and Why is it Important?

The BUN/Creatinine ratio is a valuable diagnostic tool that provides insight into kidney function and overall metabolic health. BUN (blood urea nitrogen) and creatinine are two key markers measured in blood tests that, when analyzed together, can reveal important information about a person’s health status.

BUN is a waste product created when the liver processes protein, while creatinine is produced from the normal breakdown of muscle tissue. Both are typically filtered out by the kidneys, making them useful indicators of kidney function.

How is the BUN/Creatinine Ratio Calculated?

The ratio is calculated by dividing the BUN value by the creatinine value, both measured in milligrams per deciliter (mg/dL). This ratio helps healthcare professionals distinguish between kidney-related issues and other conditions that might affect these individual markers.

Understanding the Normal Range for BUN/Creatinine Ratio

A healthy BUN/Creatinine ratio typically falls between 10:1 to 20:1. However, it’s important to note that the normal range can vary slightly depending on factors such as age, gender, and muscle mass.

• Normal range: 10:1 to 20:1
• Low ratio: Below 10:1
• High ratio: Above 20:1

What factors can influence the BUN/Creatinine ratio? Age is a significant factor, with the ratio tending to increase as we get older. Additionally, muscle mass plays a role, as individuals with less muscle mass may have lower creatinine levels, potentially affecting the ratio.

Causes and Implications of a Low BUN/Creatinine Ratio

A low BUN/Creatinine ratio (below 10:1) can be indicative of various health issues. What are some common causes of a low ratio?

1. Malnutrition or low protein intake
2. Advanced liver disease
3. Sickle cell anemia
4. Overhydration
5. Pregnancy (especially in the later stages)

How does malnutrition affect the BUN/Creatinine ratio? When protein intake is insufficient, the liver produces less urea, resulting in lower BUN levels. This can cause the ratio to decrease, even if creatinine levels remain stable.

In cases of advanced liver disease, the organ’s ability to produce urea is compromised, leading to lower BUN levels and subsequently, a lower ratio. Sickle cell anemia can also contribute to a low ratio as the kidneys may reabsorb less urea, causing more to be excreted in the urine.

High BUN/Creatinine Ratio: Causes and Health Implications

A BUN/Creatinine ratio above 20:1 is considered high and may indicate various health concerns. What are some common causes of an elevated ratio?

• Dehydration
• Congestive heart failure
• Gastrointestinal bleeding
• Shock
• Urinary tract obstruction
• Certain medications (e.g., corticosteroids, tetracyclines)

How does dehydration affect the BUN/Creatinine ratio? When the body is dehydrated, the kidneys conserve water by reabsorbing more urea, leading to higher BUN levels. This increase in BUN without a corresponding increase in creatinine results in a higher ratio.

In cases of congestive heart failure, reduced blood flow to the kidneys can cause BUN levels to rise more rapidly than creatinine levels, elevating the ratio. Gastrointestinal bleeding can also increase the ratio as the breakdown of blood in the digestive tract leads to higher protein metabolism and subsequent BUN production.

Interpreting BUN and Creatinine Levels Individually

While the BUN/Creatinine ratio provides valuable insights, it’s also important to consider BUN and creatinine levels individually. What do these individual markers indicate?

BUN (Blood Urea Nitrogen)

BUN levels typically range from 7 to 20 mg/dL. Elevated BUN levels can suggest kidney dysfunction, dehydration, or increased protein catabolism. Conversely, low BUN levels might indicate liver problems, overhydration, or malnutrition.

Creatinine

Normal creatinine levels usually fall between 0.6 to 1.2 mg/dL for men and 0.5 to 1.1 mg/dL for women. Elevated creatinine levels often indicate kidney problems, while low levels might suggest decreased muscle mass or liver disease.

How do these individual markers complement the BUN/Creatinine ratio? By examining both the ratio and individual levels, healthcare providers can gain a more comprehensive understanding of a patient’s metabolic and kidney function.

Improving Your BUN/Creatinine Ratio: Lifestyle and Dietary Considerations

While medical intervention may be necessary in some cases, there are several lifestyle and dietary changes that can help maintain a healthy BUN/Creatinine ratio. What steps can individuals take to improve their ratio?

1. Stay hydrated: Proper hydration helps maintain optimal kidney function and prevents BUN levels from rising due to dehydration.
2. Balanced protein intake: Consume an appropriate amount of protein based on your individual needs and health status.
3. Regular exercise: Physical activity helps maintain muscle mass, which can positively influence creatinine levels.
4. Limit alcohol consumption: Excessive alcohol intake can strain the liver and kidneys, potentially affecting BUN and creatinine levels.
5. Manage underlying health conditions: Properly treating conditions like diabetes and hypertension can help maintain kidney health.

How does hydration impact the BUN/Creatinine ratio? Adequate fluid intake helps the kidneys efficiently filter waste products, preventing unnecessary increases in BUN levels. This can help maintain a balanced ratio and support overall kidney function.

When to Seek Medical Attention for Abnormal BUN/Creatinine Ratios

While minor fluctuations in the BUN/Creatinine ratio can occur due to various factors, significant or persistent abnormalities may warrant medical attention. What signs should prompt individuals to consult a healthcare provider?

• Consistently high or low ratios on multiple tests
• Sudden, significant changes in the ratio
• Accompanying symptoms such as fatigue, swelling, changes in urination patterns, or unexplained weight loss
• Known risk factors for kidney disease, such as diabetes or hypertension

How often should individuals have their BUN/Creatinine ratio checked? For those without known health issues, annual check-ups usually suffice. However, individuals with chronic conditions affecting kidney function may require more frequent monitoring as advised by their healthcare provider.

The Role of BUN/Creatinine Ratio in Diagnosing Kidney Disease

The BUN/Creatinine ratio plays a crucial role in the diagnosis and monitoring of kidney disease. How do healthcare providers use this ratio to assess kidney function?

In the early stages of kidney disease, the ratio may remain within the normal range as both BUN and creatinine levels rise proportionally. However, as the condition progresses, BUN levels often increase more rapidly than creatinine, leading to an elevated ratio.

What other tests are typically used in conjunction with the BUN/Creatinine ratio to diagnose kidney disease?

• Glomerular Filtration Rate (GFR): This test estimates how much blood passes through the glomeruli (tiny filters in the kidneys) each minute.
• Urine albumin-to-creatinine ratio: This test checks for the presence of albumin in the urine, which can indicate kidney damage.
• Imaging studies: Ultrasounds or CT scans can provide visual information about kidney structure and function.

How does the BUN/Creatinine ratio complement these other tests? While the ratio provides valuable information about kidney function and overall metabolism, it’s most effective when considered alongside other diagnostic tools. This comprehensive approach allows for a more accurate assessment of kidney health and function.

BUN/Creatinine Ratio in Special Populations

The interpretation of the BUN/Creatinine ratio may vary for certain populations due to unique physiological factors. How does the ratio differ in these special groups?

Elderly Individuals

Older adults tend to have higher BUN/Creatinine ratios due to age-related changes in kidney function and decreased muscle mass. What is considered a normal ratio for the elderly?

While the standard range of 10:1 to 20:1 still applies, ratios up to 30:1 may be considered acceptable in some elderly individuals, depending on their overall health status and other clinical factors.

Pregnant Women

Pregnancy can significantly affect the BUN/Creatinine ratio. How does pregnancy impact these levels?

During pregnancy, increased glomerular filtration rate and plasma volume expansion can lead to lower BUN levels. Creatinine levels may also decrease slightly. As a result, pregnant women often have lower BUN/Creatinine ratios, especially in the later stages of pregnancy.

Athletes and Bodybuilders

Individuals with high muscle mass, such as athletes and bodybuilders, may have unique BUN/Creatinine profiles. How does increased muscle mass affect the ratio?

Higher muscle mass typically leads to increased creatinine production, which can result in lower BUN/Creatinine ratios. However, high protein diets common among athletes may also increase BUN levels, potentially balancing out the ratio.

Why is it important for healthcare providers to consider these factors when interpreting BUN/Creatinine ratios in special populations? Understanding the physiological differences in these groups helps prevent misdiagnosis and ensures appropriate interpretation of test results.

The Future of BUN/Creatinine Ratio in Medical Diagnostics

As medical science advances, our understanding and utilization of the BUN/Creatinine ratio continue to evolve. What developments can we expect in the future regarding this diagnostic tool?

Integration with Artificial Intelligence

How might AI enhance the interpretation of BUN/Creatinine ratios? Artificial intelligence algorithms could potentially analyze vast amounts of patient data to identify subtle patterns and correlations, improving the accuracy of diagnoses based on BUN/Creatinine ratios and other biomarkers.

Personalized Medicine

How could the BUN/Creatinine ratio contribute to personalized medicine approaches? As our understanding of individual genetic and physiological variations grows, the interpretation of BUN/Creatinine ratios may become more tailored to each patient’s unique profile, leading to more precise diagnoses and treatment plans.

Novel Biomarkers

What new biomarkers might complement or enhance the BUN/Creatinine ratio in the future? Researchers are continuously investigating new markers of kidney function and metabolic health. These could potentially be used in conjunction with the BUN/Creatinine ratio to provide a more comprehensive picture of an individual’s health status.

How might these advancements impact patient care? By improving the accuracy and specificity of diagnoses based on the BUN/Creatinine ratio and related markers, these developments could lead to earlier detection of kidney issues and more targeted treatment strategies.

BUN/Creatinine Ratio: High & Low Levels + Normal Range

Written by Joe Cohen, BS | Last updated:

December 15, 2022

Medically reviewed by

Biljana Novkovic, PhD, Jonathan Ritter, PharmD, PhD (Pharmacology)
| Written by Joe Cohen, BS | Last updated:

December 15, 2022

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BUN (blood urea nitrogen) and creatinine are two blood tests that can reveal a lot about your metabolism, kidney, liver, and overall health. And while they can be used separately, the BUN/creatinine ratio can help pinpoint important issues. Learn more about the BUN/creatinine ratio and what it can reveal about your health.

What is the BUN/Creatinine Ratio?

BUN (blood urea nitrogen) and creatinine are two lab tests that are often ordered as part of a comprehensive metabolic panel. Your doctor may order this panel to get an idea of your overall health and metabolism.

BUN measures the amount of urea in your blood. Urea is a waste product made in the liver as the body processes protein. This protein is mostly derived from the diet, but it can also result from tissue protein turnover [1, 2, 3].

Urea is removed by the kidneys, but the rate of removal depends on the needs of the body. The kidneys can return different amounts of urea into the bloodstream depending on factors such as hydration and blood pressure. High urea is an important marker of kidney dysfunction as well [1, 2, 3].

Creatinine, on the other hand, is a waste product created from the normal wear and tear of muscles. It is produced from creatine, a protein that helps generate energy for muscle contractions. Creatinine production essentially reflects muscle mass, and because this mass changes little from day to day, creatinine production tends to be fairly constant [3, 4, 5].

Creatinine is removed from the body by the kidneys, which filter almost all of it from the blood into the urine, at a fairly constant rate. That is why blood levels are usually a good indicator of how well your kidneys are working [3, 4, 5].

So to recap, BUN levels fluctuate, while creatinine is removed at a constant rate and its blood levels are usually stable. That’s why the BUN/Creatinine ratio can be used to check for issues such as dehydration, kidney injury/disease, gut bleeding, and other problems [3].

BUN/Creatinine Ratio Normal Range

The normal range for BUN/Creatinine ratio is anywhere between 5 – 20 mg/dL.

BUN/Creatinine ratio increases with age, and with decreasing muscle mass [6].

Low BUN/Creatinine Ratio

A low BUN/Creatinine ratio indicates an underlying disease/disorder and will usually be accompanied by the symptoms of this underlying disorder. The causes shown here are commonly associated with low BUN/creatinine. Work with your doctor or other health care professional for an accurate diagnosis.

A BUN/Creatinine ratio lower than normal can be caused by:

• Low protein intake, seen in conditions of malnutrition and starvation. Less protein means lower BUN production [3].
• Advanced liver disease, when the liver can’t produce enough urea, resulting in lower BUN levels [3].
• Sickle cell anemia – in this condition kidneys reabsorb less urea and more of it is lost in the urine, resulting in lower BUN [3].
• Hypothyroidism, a condition where the thyroid glands do not produce enough thyroid hormone. This condition can increase creatinine levels [7, 8].
• Rhabdomyolysis, a condition in which damaged muscles breaks down rapidly, resulting in higher creatinine levels [3].
• Kidney damage and kidney failure. When kidneys become impaired for any reason, creatinine blood levels will rise [9].
• Drugs such as acetazolamide, a diuretic used to treat various conditions including glaucoma, epilepsy, altitude sickness, and heart failure [10].

High BUN/Creatinine Ratio

A high BUN/Creatinine ratio indicates an underlying disease/disorder and will usually be accompanied by the symptoms of this underlying disorder. The causes shown here are commonly associated with high BUN/creatinine. Work with your doctor or other health care professional for an accurate diagnosis.

A BUN/Creatinine ratio above the normal range can be caused by:

• Dehydration. Dehydration increases the blood levels of both BUN and creatinine but increases BUN more than creatinine [11].
• Gut bleeding. The blood in the gut gets digested and this increases the amount of protein and BUN levels [12, 13].
• Hyperthyroidism. This condition can increase BUN and lower creatinine levels [7].
• Congestive heart failure – heart failure increases the reabsorption of urea and increases blood BUN levels [14, 15].
• Kidney disease, it can increase BUN as well as creatinine levels [16].
• Drugs such as tetracycline (an antibiotic) or corticosteroids (used to treat inflammation) [10, 3, 17].

Factors that Increase BUN/Creatinine Ratio

It is important to address any health condition that may be causing the disbalance. Once the condition has been resolved, the BUN/creatinine ratio should return to a normal range. Your doctor will work to find an accurate diagnosis and an appropriate treatment plan, which may include some of the strategies below. Never use any of these in place of what your doctor prescribes.

Factors that Increase BUN

• Increasing dietary protein. Low BUN levels may mean that you are not consuming enough protein. If this is the case, try to increase your consumption of high-protein foods like lean meats and beans [1].
• Reducing alcohol consumption. Alcohol blocks the production of urea (BUN) [18].

Factors that Decrease Creatinine

• Avoiding creatine and creatine-based supplements
• Increasing dietary fiber. Vegetable and fruit fiber improves kidney health and can lower blood creatinine levels [19].
• Losing some weight if overweight. Weight loss can improve your kidney health and decrease creatinine levels [20].

How to Decrease Your BUN/Creatinine Ratio

Again, disbalance between BUN and creatinine is often due to a serious medical condition and it is important to address it. Once the condition gets resolved, the BUN/creatinine ratio will go back into the normal range. Your doctor will work to find an accurate diagnosis and an appropriate treatment plan, which may include some of the strategies below. Never use any of these in place of what your doctor prescribes.

Factors that Decrease Bun

• Drinking more water. Make sure you are properly hydrated.
• Losing weight if overweight. A high BMI can cause kidney dysfunction and increase BUN (urea) levels [21, 22, 23].

Factors that Increase Creatinine

• Increasing physical activity (unless it’s not recommended due to an existing medical condition) – exercise increases creatinine levels + it helps build muscle [24, 25].
• Avoid alcohol. It may decrease blood creatinine [26, 27].

Contents

• What is the BUN/Creatinine Ratio?

  • BUN/Creatinine Ratio Normal Range

  • Low BUN/Creatinine Ratio

  • High BUN/Creatinine Ratio

• Factors that Increase BUN/Creatinine Ratio

  • Factors that Increase BUN

  • Factors that Decrease Creatinine

• How to Decrease Your BUN/Creatinine Ratio

  • Factors that Decrease Bun

  • Factors that Increase Creatinine

BUN and Creatinine – Clinical Methods

Definition

Urea and creatinine are nitrogenous end products of metabolism. Urea is the primary metabolite derived from dietary protein and tissue protein turnover. Creatinine is the product of muscle creatine catabolism. Both are relatively small molecules (60 and 113 daltons, respectively) that distribute throughout total body water. In Europe, the whole urea molecule is assayed, whereas in the United States only the nitrogen component of urea (the blood or serum urea nitrogen, i.e., BUN or SUN) is measured. The BUN, then, is roughly one-half (28/60 or 0.446) of the blood urea.

The normal range of urea nitrogen in blood or serum is 5 to 20 mg/dl, or 1.8 to 7.1 mmol urea per liter. The range is wide because of normal variations due to protein intake, endogenous protein catabolism, state of hydration, hepatic urea synthesis, and renal urea excretion. A BUN of 15 mg/dl would represent significantly impaired function for a woman in the thirtieth week of gestation. Her higher glomerular filtration rate (GFR), expanded extracellular fluid volume, and anabolism in the developing fetus contribute to her relatively low BUN of 5 to 7 mg/dl. In contrast, the rugged rancher who eats in excess of 125 g protein each day may have a normal BUN of 20 mg/dl.

The normal serum creatinine (^sCr) varies with the subject’s body muscle mass and with the technique used to measure it. For the adult male, the normal range is 0.6 to 1.2 mg/dl, or 53 to 106 μmol/L by the kinetic or enzymatic method, and 0.8 to 1.5 mg/dl, or 70 to 133 μmol/L by the older manual Jaffé reaction. For the adult female, with her generally lower muscle mass, the normal range is 0.5 to 1.1 mg/dl, or 44 to 97 μmol/L by the enzymatic method.

Technique

Multiple methods for analysis of BUN and creatinine have evolved over the years. Most of those in current use are automated and give clinically reliable and reproducible results.

There are two general methods for the measurement of urea nitrogen. The diacetyl, or Fearon, reaction develops a yellow chromogen with urea, and this is quantified by photometry. It has been modified for use in autoanalyzers and generally gives relatively accurate results. It still has limited specificity, however, as illustrated by spurious elevations with sulfonylurea compounds, and by colorimetric interference from hemoglobin when whole blood is used.

In the more specific enzymatic methods, the enzyme urease converts urea to ammonia and carbonic acid. These products, which are proportional to the concentration of urea in the sample, are assayed in a variety of systems, some of which are automated. One system checks the decrease in absorbance at 340 mm when the ammonia reacts with alpha-ketoglutaric acid. The Astra system measures the rate of increase in conductivity of the solution in which urea is hydrolyzed.

Even though the test is now performed mostly on serum, the term BUN is still retained by convention. The specimen should not be collected in tubes containing sodium fluoride because the fluoride inhibits urease. Also chloral hydrate and guanethidine have been observed to increase BUN values.

The 1886 Jaffé reaction, in which creatinine is treated with an alkaline picrate solution to yield a red complex, is still the basis of most commonly used methods for measuring creatinine. This reaction is nonspecific and subject to interference from many noncreatinine chromogens, including acetone, acetoacetate, pyruvate, ascorbic acid, glucose, cephalosporins, barbiturates, and protein. It is also sensitive to pH and temperature changes. One or another of the many modifications designed to nullify these sources of error is used in most clinical laboratories today. For example, the recent kinetic-rate modification, which isolates the brief time interval during which only true creatinine contributes to total color formation, is the basis of the Astra modular system.

More specific, non-Jaffé assays have also been developed. One of these, an automated dry-slide enzymatic method, measures ammonia generated when creatinine is hydrolyzed by creatinine iminohydrolase. Its simplicity, precision, and speed highly recommend it for routine use in the clinical laboratory. Only 5-fluorocytosine interferes significantly with the test.

Creatinine must be determined in plasma or serum and not whole blood because erythrocytes contain considerable amounts of noncreatinine chromogens. To minimize the conversion of creatine to creatinine, specimens must be as fresh as possible and maintained at pH 7 during storage.

Basic Science

More than 99% of urea synthesis occurs in the liver. Its primary source is dietary protein. In the gut, the protein is converted into peptides and amino acids, more than 90% of which are absorbed and carried to the liver. In the hepatocyte, the amino acids are deaminated and transaminated. The resulting excess nitrogen feeds into the urea cycle to be incorporated into urea. The protein moieties escaping absorption by the small bowel, plus recycled urea, are converted into ammonia by gut flora predominantly in the colon. The ammonia diffuses through the portal circulation into the liver to enter the urea cycle ().

Figure 193.1

Absorption, metabolism, and excretion of urea. (Modified from Raforth and Onstad, 1975.)

The amount of urea produced varies with substrate delivery to the liver and the adequacy of liver function. It is increased by a high-protein diet, by gastrointestinal bleeding (based on plasma protein level of 7.5 g/dl and a hemoglobin of 15 g/dl, 500 ml of whole blood is equivalent to 100 g protein), by catabolic processes such as fever or infection, and by antianabolic drugs such as tetracyclines (except doxycycline) or glucocorticoids. It is decreased by low-protein diet, malnutrition or starvation, and by impaired metabolic activity in the liver due to parenchymal liver disease or, rarely, to congenital deficiency of urea cycle enzymes. The normal subject on a 70 g protein diet produces about 12 g of urea each day.

This newly synthesized urea distributes throughout total body water. Some of it is recycled through the enterohepatic circulation. Usually, a small amount (less than 0.5 g/day) is lost through the gastrointestinal tract, lungs, and skin; during exercise, a substantial fraction may be excreted in sweat. The bulk of the urea, about 10 gm each day, is excreted by the kidney in a process that begins with glomerular filtration. At high urine flow rates (greater than 2 ml/min), 40% of the filtered load is reabsorbed, and at flow rates lower than 2 ml/min, reabsorption may increase to 60%. Low flow, as in urinary tract obstruction, allows more time for reabsorption and is often associated with increases in antidiuretic hormone (ADH), which increases the permeability of the terminal collecting tubule to urea. During ADH-induced antidiuresis, urea secretion contributes to the intratubular concentration of urea. The subsequent buildup of urea in the inner medulla is critical to the process of urinary concentration. Reabsorption is also increased by volume contraction, reduced renal plasma flow as in congestive heart failure, and decreased glomerular filtration.

Creatinine formation begins with the transamidination from arginine to glycine to form glycocyamine or guanidoacetic acid (GAA). This reaction occurs primarily in the kidneys, but also in the mucosa of the small intestine and the pancreas. The GAA is transported to the liver where it is methylated by S-adenosyl methionine (SAM) to form creatine. Creatine enters the circulation, and 90% of it is taken up and stored by muscle tissue. In a reaction catalyzed by creatine phosphokinase (CPK), most of this muscle creatine is phosphorylated to creatine phosphate. Each day, about 2% of these stores is converted nonenzymatically and irreversibly to creatinine ().

Figure 193.2

Metabolism and excretion of creatinine. (Modified from Dosseter, 1966.)

Thus, creatinine production essentially reflects lean body mass. Because this mass changes little from day to day, the production rate is fairly constant. Absolute creatinine production declines with age in line with decreasing muscle mass. Unlike urea, creatinine is largely unaffected by gastrointestinal bleeding or by catabolic factors such as fever and steroids. However, the ingestion of cooked meat can raise the ^sCr because cooking converts the creatine in meat to creatinine. Certain drugs, notably the psychoactive phenacemide, can increase the production rate.

Like urea, creatinine distributes throughout total body water. Its concentration in serum is a function of the usually constant production and excretion rates. It may be slightly higher in the evening than in the morning, due most likely to dietary meat intake by day.

In normal subjects, creatinine is excreted primarily by the kidneys. There is minimal extrarenal disposal or demonstrable metabolism. As a small molecule (molecular weight of 113 daltons), it is freely filtered by the glomerulus. Unlike urea, it is not reabsorbed or affected by urine flow rate. It is normally secreted by the tubules in a small but significant amount (up to 10% of total excretion). Excretion of both urea and creatinine is increased during exercise without producing significant change in serum concentration. The total creatinine excretion in a normal man averages 14 to 26 mg/kg/day, and in a normal woman 11 to 20 mg/kg/day. Excretion declines with age, and is about 10 mg/kg/day in a 90-year-old man. However, it should not vary more than 10 to 15% in a given individual. The amount excreted has been used as a rough index of the completeness of daily urine collection.

Measurement of urine creatinine excretion is used in calculating the creatinine clearance (^cCr). Short of the more precise but technically impractical inulin clearance, the ^cCr is the standard clinical tool for estimating GFR, especially in the early stages of renal disease. In that setting ^sCr and BUN are not very useful indices of GFR due to their parabolic relationship and to the wide range of normal ().

Figure 193.3

Relationship of blood urea nitrogen or serum creatinine to glomerular filtration rate.

In contrast, the ^cCr has the major disadvantage of inaccuracies in urine collection, especially during short-term clearances or in patients with low urine volumes. For this reason, 24-hour clearances are preferred for general use, because the usually larger volumes will minimize errors of collection. The concentration of creatinine in the serum and urine is determined, and with careful attention to the units of measurement, the ^cCr is calculated as follows:

where ^uCr = urine creatinine concentration in mg/dl, V = urine volume in ml/min, and ^sCr = serum creatinine concentration in mg/dl. The result may then be standardized to 1.73 m² body surface area (BSA).

The subject’s BSA is related to weight and height and is usually obtained from a nomogram. Example:

Several shortcuts to estimate the ^cCr without collecting urine have been proposed. The earliest and probably the least accurate ignores the subject’s age and weight, and simply divides 100 by the ^sCr. The Cockcroft-Gault formula is the one usually recommended for use in calculating dosage of drugs (especially nephrotoxic antibiotics). It takes into account the well-documented fall in GRF with age as follows:

In advanced renal failure, net creatinine excretion decreases significantly. Even though tubular secretion increases as GFR falls, it does not compensate for the decrease in filtration when the GFR is below 50 ml/min/1.73 m². Further, there is measurable creatinine metabolism by gut flora and, in some patients, decreased creatinine synthesis. Thus ^cCr is unreliable and often overestimates GFR in chronic renal failure and in cirrhosis. It has been suggested that, when the GFR is below 15 ml/min, the mean of ^cCr plus urea clearance gives a more accurate index of GFR. Thus:

Certain drugs may affect ^cCr without changing GFR. Salicylates, cimetidine, and trimethoprim interfere with tubular secretion of creatinine and cause a spuriously low ^cCr.

Clinical Significance

The BUN and ^sCr are screening tests of renal function. Because they are handled primarily by glomerular filtration with little or no renal regulation or adaptation in the course of declining renal function, they essentially reflect GFR. Unfortunately, their relation to GRF is not a straight line but rather a parabolic curve (). Their values remain within the normal range until more than 50% of renal function is lost. Within that range, however, a doubling of the values (e.g., BUN rising from 8 to 16 mg/dl or ^sCr from 0.6 to 1.2 mg/dl) may mean a 50% fall in the GFR. Therefore, in the early stages of renal disease, these tests could create a false sense of security. Random values above the midrange of normal should be corroborated by a normal ^cCr before one can confidently tell a patient that his or her kidney function is normal.

At the other end of the curve, small changes in kidney function can produce large increments in BUN and ^sCr. Here, these tests are generally adequate to follow a patient’s course. Indeed, the reciprocal of the ^sCr plotted against time shows a straight-line progression of renal disease in each individual patient, and can be used to predict the advent of end-stage renal disease.

At all stages of renal insufficiency, the ^sCr is a much more reliable indicator of renal function than the BUN because the BUN is far more likely to be affected by dietary and physiologic conditions not related to renal function (). For example patients with congestive heart failure and intact kidneys commonly present with a BUN of 50 to 70 mg/dl and an ^sCr below 1.2 mg/dl. Of course, ^sCr may rise under some of these extrarenal factors, but seldom will it exceed 3 to 4 mg/dl. The stages of renal failure have been defined according to the ^sCr as follows:

Table 193.1

Extrarenal Factors Affecting BUN and ^sCr.

With so many limitations on the usefulness of the BUN, one wonders why the test survives. When taken with the ^sCr, it is a very useful clue to the presence of a prerenal or postrenal component to azotemia. Other factors being normal, a patient with an ^sCr of 5.0 mg/dl would be expected to have a BUN close to 50 mg/dl. If the BUN is 100 mg/dl instead, then the clinician should begin a search for extrarenal factors (). Note that this 10 to 1 ratio applies best in moderate to advanced renal failure. Attention to these reversible complications of uremia can give a patient a reprieve from an untimely sentence of end-stage renal disease.

A low BUN/Cr ratio suggests inadequate protein intake, reduced urea synthesis as in advanced liver disease, supernormal excretion of urea as in sickle cell anemia, increased creatinine production as in rhabdomyolysis, or more effective removal of urea than creatinine during dialysis.

The BUN survives and is finding wide application in the nutritional management of critically ill patients. The urea nitrogen appearance (UNA) objectively lets the intensivist know whether the patient’s nitrogen needs are being met. The UNA assessment requires the measurement of BUN at the beginning and end of the period of observation as well as the total urea excretion.

where

The BUN and creatinine, taken together, are valuable screening tests in evaluating renal disease. Though they may fall short as absolute indicators of renal function at any-given point in time, they are useful in following progression of disease.

References

1. Bauer JH, Brooks CS, Burch RN. Renal function studies in man with advanced renal insufficiency. Am J Kidney Dis. 1982;11:30–35. [PubMed: 7102662]

2. Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16:31–41. [PubMed: 1244564]

3. Doolan PD, Alpen EL, Theil GB. A clinical appraisal of the plasma concentration and endogenous clearance of creatinine. Am J Med. 1962;32:65–79. [PubMed: 13887292]

4. Dosseter JB. Creatininemia versus uremia. Ann Intern Med. 1966;65:1287–99. [PubMed: 5928490]

5. Kassirer JP. Clinical evaluation of kidney function: glomerular function. N Engl J Med. 1971;285:355–89. [PubMed: 4933769]

6. Mitch WE, Collier WU, Walser M. Creatinine metabolism in chronic renal failure. Clin Sci. 1980;58:327–35. [PubMed: 7379458]

7. Narayanan S, Appleton HD. Creatinine: a review. Clin Chem. 1980;26:1119–26. [PubMed: 6156031]

8. Raforth RJ, Onstad GR. Urea synthesis after oral protein ingestion in man. J Clin Invest. 1975;56:1170–74. [PMC free article: PMC301980] [PubMed: 1184743]

what does this mean, norms and causes of increased rates

What is creatinine?

Creatinine is a chemical compound in the human body, which is formed during the breakdown of protein molecules. The substance is part of the residual nitrogen. The beginning of the chain is creatine, a component that moves throughout the body, starting from the renal parenchyma.

The methylation process takes place in the liver. After that, creatine enters the muscles, where it is converted to creatine phosphate. The latter enters the myofibrils and decomposes into phosphate and creatinine. Muscles receive energy for contraction. The rest goes into the blood. In the liver, creatinine is not converted and is easily excreted in the urine. Energy turnover is constantly happening. In a healthy body, the amount of a substance is always stable.

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Depending on the health of the kidneys and the state of the muscles, the level of creatinine changes. A decrease in this substance in the blood is required with increased breakdown of muscle tissue. This happens in the case of kidney failure, when it becomes difficult for the body to remove toxic substances.

A person can detect a deviation of creatinine from the norm independently according to the specific signs of the body. For example, kidney pathology leads to a change in the color of urine. It acquires a cloudy color, a brown tint or a shade of coffee grounds. The patient begins to go to the toilet less often, the volume of urine decreases. A typical symptom is the accumulation of fluid in the abdominal cavity and swelling of the face and extremities.

When urinating, it hurts a person, he feels pain. Pain when the situation worsens may appear in the hypochondrium or in the lumbar region. People get tired quickly, when they wake up they immediately feel weak, appetite decreases, attention is disturbed, it is difficult to concentrate on one thing. Insomnia appears, blood pressure either goes down or goes up. Infectious lesions of the kidneys are accompanied by fever.

Creatinine norm

The norm of creatinine depends entirely on the level of accumulation of muscle mass in the body. The indicator is usually denoted in microcol / l. Normative values ​​are not the same throughout life. In men with good health, the rate is always higher than that of women. In general, for children and adults, the following standard indicators can be compiled, measured in µmol / l:

• in women under 60 years old – 53-97, over 60 years old – 53-106;
• in men under 60 years old – 80-115, over 60 years old – 71-115;
• in children in the newborn state – 27-88, up to 1 year – 18-35, from one year to 10 years – 27-62 and from 10 to 18 years – 44-88.

The required amount of a substance is calculated based on the total mass of a person, the level of his physical endurance, activity in everyday life. What causes the fact that the norm of creatinine in a blood test for men, women and children is significantly different.

Gender, weight, age of the patient are mandatory criteria for evaluation. This makes it possible to classify a biochemical blood test for creatinine as an exclusively primary diagnostic method. It is noted that the criterion is characterized by a greater degree of sensitivity to kidney pathologies than urea.

It should be understood that creatinine can decrease not only against the background of pathological problems. Strong physical overstrain or overwork will certainly affect the analysis. This includes the delivery of creatinine after several days of feasting, where predominantly meat food prevailed and there was a lot of alcohol.

If there has been a state of dehydration, leading to thickening of the blood, then the creatinine level temporarily increases. Many drugs, if taken uncontrollably, can have a toxic effect on the urinary organs.

Indications for creatinine testing

Creatinine analysis helps to evaluate the filtration function of the kidneys. It is also prescribed for severe injuries and diagnosed diseases of varying degrees of course. It also allows you to evaluate the efficiency of renal filtration of small molecules and to diagnose the glomerular filtration rate. The main indications are:

• known renal insufficiency or suspected disease;
• different degrees of kidney disease, including pyelonephritis, polycystic disease, urolithiasis, glomerulonephritis;
• burns and injuries;
• muscle atrophy;
• endocrine diseases;
• problems with the cardiovascular system;
• acute inflammation;
• sepsis;
• recovery period after surgical interventions.

Preparing for a creatinine test

Biochemical analysis is carried out with a certain preparation. Firstly, it is done on an empty stomach and always in the morning. The day before the analysis, the last time they eat is no later than 20 pm. And in one day it is important to comply with the following conditions:

• do not stress and get enough sleep;
• do not overwork physically and do not do complex exercises, such as push-ups with dumbbells;
• avoid overheating, including sauna visits;
• do not drink alcoholic beverages;
• do not eat fatty foods and try to eat less meat;
• avoid spicy and salty foods;
• do not smoke 2 hours before the analysis.

Incorrect sampling of biomaterial can lead to unreliable results. This leads to the destruction of red blood cells. Their contents are released. The result is a distorted biochemical composition of the blood. In this case, a retest is simply necessary.

False positive results can occur in the presence of a large amount of muscle mass. If a weightlifter passes the diagnosis, then this fact should be taken into account. The result is affected by diabetes mellitus in the patient’s history, against which the concentration of simple sugars, acetone and urea increases. With muscle damage, as well as against the background of taking medications such as barbiturates or aminoglycoside antibiotics, creatinine readings are distorted.

Elevated creatinine

A person is in energy exchange throughout his life. A slight deviation of creatinine from the norm is not considered a problem. But if this excess is significant and is observed regularly, then there are definitely problems.

An increase in creatinine is indicated by weakness, drowsiness and loss of strength. You may feel dizzy and have a nausea reflex. Breathing quickens, a person does not get fresh air. These are indirect signs of kidney failure with a high level of creatinine in the blood. May indicate inflammation and destruction in the muscular system, infectious diseases leading to kidney damage.

What does elevated creatinine mean?

Elevated creatinine in human blood can be associated with two reasons: physiological or pathological. The first option is associated with a large amount of muscle mass as a result of intense physical exercise. Such cases occur among people who do a lot and often do wrestling, powerlifting and bodybuilding.

Those who cannot imagine life without meat are also prone to increased creatinine levels. In many cases, the uncontrolled use of drugs leads to the need to reduce the creatinine level. It is especially dangerous to use tetracycline antibiotics, cephalosporins, non-steroidal anti-inflammatory drugs without the advice of a doctor.

Elevated creatinine can also speak of pathological disorders in the body. For example, an increase in the rate is often observed in case of kidney diseases in the acute and chronic stages, as well as in violation of the patency of the urinary tract. The kidneys can suffer due to impaired blood supply, which sooner or later leads to serious pathologies of the cardiovascular system.

Radiation sickness or oncological diseases can lead to constant jumps in creatinine. Septic shock, burns of varying severity, as well as diagnosed endocrine pathologies can cause changes in the indicator.

Causes of elevated creatinine

The main reason for the increase in the indicator is its increased production or poor excretion process from the body. This phenomenon is typical when diagnosing the following pathologies:

• liver problems, including inflammation, toxic poisoning and cirrhosis;
• necrosis of internal organs due to damage to cells and tissues;
• renal insufficiency;
• increased level of the thyroid gland;
• muscle and bone lesions;
• second and third degree burns;
• vascular lesions in the kidneys;
• complication after diabetes mellitus;
• weakness of the muscular system;
• diseases of the pulmonary system;
• fever;
• drug poisoning, manifested by toxic effects on the kidneys.

Fasting, pregnancy and long-term treatment with corticosteroids can cause temporary phenomena of an increase in the indicator.

How to lower blood creatinine?

It is almost impossible to lower the blood count on your own. This is due to the fact that one cannot do without passing certain tests and consulting with a specialist. It is important to adhere to competent treatment and limit nutrition in accordance with the recommendations of the doctor. During the diagnosis, a serious pathology may be revealed, without the treatment of which it is impossible to adjust the level of creatinine in the blood.

If a patient’s creatinine is elevated as a result of improper and unbalanced nutrition, then in order to restore the indicator, it is necessary to abandon the use of a number of products. These include primarily fatty meats and fish, smoked and spicy foods, dairy products, cheeses, salt, sugar, and strong drinks such as coffee and black tea.

The food should contain a minimum of protein and salt. Try to eat foods that contain antioxidants. These include cabbage, beans, walnuts, pistachios, strawberries, oranges, tangerines, eggplants. Drink at least a liter of pure water per day. Specialists can prescribe a course of taking special drugs that will help to cope with the problem quickly and efficiently.

It should be temporarily canceled toxic drugs and anabolic hormones. In case of kidney failure or in case of serious injury, special treatment is prescribed. It is important to restore the patency of the renal tubules and normalize blood flow. The damaged surface will close faster and the shock will pass. Thyrotoxicosis requires drugs that suppress excessive thyroid function.

If, after the measures taken, the indicators do not give a positive trend and a return to normal is not expected, then it is necessary to adjust the approach to treatment. Perhaps the connection of fasting days is required to reduce the load on the organs and urinary systems.

Creatinine decreased

When an amino acid is used by the body for energy, part of it is consumed according to needs. The remaining creatinine remains as waste. Decreased creatinine is often seen in vegetarians and pregnant women. In the first case, the problem is the lack of animal products, leading to protein deficiency in the body, and consequently, to muscle weakness with subsequent atrophy. During the bearing of a child, a physiological mechanism takes place, during which the total volume of blood increases. In many older people, this figure goes down, but should not cause concern.

Causes of low creatinine

It can be concluded that a reduced level of creatinine is observed in the following cases:

• For low muscle mass. The share of muscles may decrease against the background of a sharp weight loss. For example, during illness or due to age.
• In diseases of the liver. If the liver is not healthy, then it cannot fully produce creatinine. Chronic disease of this organ can provoke a 50% shortage of creatinine. It is easy to detect this with a simple blood test.
• Long diets. Creatinine is mostly produced naturally, but some part comes with the food you eat. If a person abruptly stops eating as before, for example, switches to a vegetarian diet, then the level of creatinine decreases rapidly.
• During childbearing. The baby also needs a lot of strength and energy for development. Mommy’s body divides all the reserves into two. Therefore, in her body, you can often fix the level of decrease in creatinine. After childbirth, this figure quickly returns to normal.

Severe weakness and the inability to perform the simplest physical exercises can indicate a low level of creatinine. With problems with the liver, the patient notices discomfort in the upper abdomen, he is sick and shivering. With a diet, weakness is accompanied by dizziness, weight quickly falls.

Creatinine blood test | The price of a blood test in Moscow

Creatinine is a chemical compound that remains after the process of energy production in the muscles. The kidneys are responsible for its filtration in the body, and after filtration it is excreted in the urine. Since it is the kidneys that maintain a normal level of creatinine in the body, its high level may indicate a violation of their functions. To confirm this diagnosis, a blood test for creatinine is required.

What determines the level of creatinine?

Its content depends on the work of the kidneys, the condition of the muscles and muscles, the age and gender of the patient. In some cases, its elevated level is detected by chance, during the delivery of a standard blood test, without the patient having symptoms. Also, in people whose levels of this substance are higher than normal, a number of symptoms may be present, including constant fatigue, dehydration, swelling, shortness of breath, neuropathy, and dry skin.

Creatinine levels can be affected by malnutrition, strict diets, and a purely plant-based diet. With age, its level decreases, so a low result of a blood test for creatinine simply speaks of age-related changes. The difference in the level of the substance depending on the sex is explained by the fact that men have more muscle mass than women. Muscular middle-aged men and athletes have more creatinine in their blood than normal people, since the level here is affected by the amount and intensity of physical activity.

People who are malnourished, who have lost weight drastically, or who have some chronic diseases, tend to lose muscle mass, which means that creatinine levels may be lower than necessary for their sex and age. Creatinine below normal can mean muscle wasting caused by anorexia or cachexia. Also, low levels are observed in pregnant women and in those who take diuretics.

When is a blood test for creatinine performed?

Small deviations of this substance from the norm are not considered a problem, since a person is always in a state of continuous energy metabolism and in the near future this excess can be used by the body. A serious increase in creatinine will require urgent action.

The body itself can do nothing with high creatinine, except to gradually remove it. If there are problems with the withdrawal, its accumulation continues and begins to have a toxic effect on all body systems, representing a health hazard. In some cases, when this process was not controlled for a long time, a very high level led patients to a mandatory blood purification procedure in order to prevent the destruction of internal organs.

The main task of taking a blood test for creatinine, recommended by the attending physician, is to identify problems in the functioning of the kidneys and urinary system, kidney failure and some hidden diseases at an early stage. So, the analysis can be assigned to:

• diagnosis, with signs of kidney disease;
• screening of kidney function in the presence of diabetes, with a disease of the cardiovascular system, complaints of high blood pressure;
• identifying side effects of certain drugs that can affect changes in kidney function;
• detection or exclusion of rhabdomyolysis – abnormal muscle breakdown;
• detection of urinary tract obstruction.
• checking the operation of the transplanted kidney, etc.

The price in Moscow of a blood test for creatinine is quite affordable, so it is important not to neglect it when recommending or prescribing such an analysis by a doctor.

How is analysis carried out at IIM?

To determine the level of creatinine, it is necessary to pass a biochemical blood test. To get an accurate result, 24 hours before the analysis, you should be away from alcohol, coffee, as well as intense physical exertion, overeating protein foods. It must be remembered that the accuracy of the result is also affected by the intake of a number of medications. The analysis is taken in the morning, before meals. Blood is taken from a vein, therefore, before the procedure, it is recommended to sit in a calm state for some time. The identified increase in the level may require a more thorough examination of the work of the kidneys.

The price of a blood test for creatinine at the Institute of Nuclear Medicine is affordable for every patient.