What is the purpose of an ALT blood test. How is the ALT test performed. What do normal ALT levels indicate. When should you be concerned about elevated ALT levels. How can you prepare for an ALT blood test. What factors can influence ALT test results. How does ALT testing contribute to overall liver health assessment.

What is Alanine Transaminase (ALT) and Its Role in Liver Function?

Alanine transaminase (ALT), also known as serum glutamate pyruvate transaminase (SGPT), is an enzyme primarily found in liver cells. This enzyme plays a crucial role in amino acid metabolism and is an essential indicator of liver health. When liver cells are damaged or die, ALT is released into the bloodstream, making it a valuable biomarker for detecting liver problems.

ALT’s primary function is to catalyze the transfer of an amino group from alanine to α-ketoglutarate, forming pyruvate and glutamate. This process is vital for energy production and protein metabolism within the liver. While ALT is predominantly found in the liver, small amounts are also present in other organs such as muscles, kidneys, and the heart.

Why is ALT important for liver health assessment?

ALT levels in the blood serve as a sensitive indicator of liver cell damage. Elevated ALT levels often suggest liver injury or disease, making it an essential component of liver function tests. Monitoring ALT levels helps healthcare providers:

• Detect early signs of liver damage
• Assess the severity of liver diseases
• Monitor the progression of liver conditions
• Evaluate the effectiveness of treatments for liver disorders

The ALT Blood Test: Procedure and Preparation

The ALT blood test is a simple and relatively painless procedure that measures the level of ALT enzyme in the blood. Here’s what you need to know about the test:

How is the ALT blood test performed?

The test involves the following steps:

1. A healthcare professional will clean the area, usually the inside of the elbow or back of the hand, with an antiseptic.
2. An elastic band is tied around the upper arm to make the vein more visible and easier to access.
3. A needle is inserted into the vein to draw a small amount of blood.
4. The blood sample is collected in a vial or tube.
5. The needle is removed, and a small bandage is applied to the puncture site.

Do you need to prepare for an ALT blood test?

Generally, no special preparation is required for an ALT blood test. However, your healthcare provider may give specific instructions based on your individual circumstances. It’s important to inform your doctor about any medications, supplements, or herbal remedies you’re taking, as some substances can affect ALT levels.

Understanding ALT Test Results: Normal Range and Interpretations

Interpreting ALT test results is crucial for assessing liver health. The normal range for ALT can vary slightly between laboratories, but generally:

What is considered a normal ALT level?

The typical normal range for ALT is between 4 to 36 units per liter (U/L). However, it’s important to note that “normal” can vary based on factors such as age, gender, and the specific testing method used by the laboratory. Always consult with your healthcare provider for the most accurate interpretation of your results.

When are ALT levels considered elevated?

ALT levels above the normal range are considered elevated. Mild elevations (typically less than 2-3 times the upper limit of normal) may not always indicate significant liver damage. However, moderate to severe elevations (more than 3 times the upper limit of normal) often suggest more serious liver issues that require further investigation.

Causes of Elevated ALT Levels: Beyond Liver Disease

While elevated ALT levels are commonly associated with liver problems, various other factors can contribute to increased ALT in the blood:

What conditions can cause ALT levels to rise?

Elevated ALT levels may be due to:

• Hepatitis (viral, alcoholic, or autoimmune)
• Cirrhosis
• Fatty liver disease
• Liver ischemia (reduced blood flow to the liver)
• Liver tumors or cancer
• Hemochromatosis (iron overload)
• Medications (certain antibiotics, statins, and pain relievers)
• Mononucleosis
• Pancreatitis
• Intense physical exercise
• Obesity

It’s important to note that elevated ALT levels alone do not provide a definitive diagnosis. Your healthcare provider will consider your medical history, symptoms, and other test results to determine the underlying cause of elevated ALT.

ALT Testing in Conjunction with Other Liver Function Tests

While ALT is a valuable indicator of liver health, it is often measured alongside other liver enzymes and proteins to provide a more comprehensive assessment of liver function.

Which other tests are commonly performed with ALT?

ALT is typically part of a panel of liver function tests that may include:

• Aspartate aminotransferase (AST)
• Alkaline phosphatase (ALP)
• Gamma-glutamyl transferase (GGT)
• Bilirubin
• Albumin
• Prothrombin time (PT)

These tests, when interpreted together, provide a more complete picture of liver health and can help identify specific liver conditions. For example, the AST/ALT ratio can be useful in distinguishing between alcoholic liver disease and other forms of liver damage.

Monitoring ALT Levels: Frequency and Importance in Liver Health Management

Regular monitoring of ALT levels is crucial for individuals with known liver conditions or those at risk of liver disease. The frequency of ALT testing depends on various factors, including the underlying condition, treatment plan, and overall health status.

How often should ALT levels be checked?

The frequency of ALT testing can vary:

• For routine health check-ups: Once a year or as recommended by your healthcare provider
• For monitoring known liver conditions: Every 3-6 months or more frequently, depending on the specific condition and treatment plan
• During medication therapy that may affect liver function: As prescribed by your doctor, which could be every few weeks to months
• After starting a new medication with potential liver effects: Initially more frequently, then less often if levels remain stable

Regular monitoring allows for early detection of liver problems and timely intervention, which can significantly improve outcomes in liver disease management.

Lifestyle Factors Affecting ALT Levels: Tips for Maintaining Liver Health

While some causes of elevated ALT levels are beyond our control, certain lifestyle factors can influence liver health and ALT levels. Understanding and addressing these factors can help maintain optimal liver function.

How can you naturally lower ALT levels and improve liver health?

Consider the following lifestyle modifications to support liver health and potentially lower ALT levels:

• Maintain a healthy weight: Obesity is strongly linked to fatty liver disease and elevated ALT levels
• Limit alcohol consumption: Excessive alcohol intake can damage liver cells and raise ALT levels
• Exercise regularly: Moderate physical activity can help reduce liver fat and improve overall liver function
• Follow a balanced diet: Focus on fruits, vegetables, whole grains, and lean proteins while limiting processed foods and saturated fats
• Stay hydrated: Adequate water intake supports liver function and helps flush toxins
• Avoid unnecessary medications: Some over-the-counter painkillers and supplements can stress the liver when used excessively
• Manage underlying conditions: Properly control conditions like diabetes and high cholesterol, which can impact liver health

By adopting these healthy lifestyle habits, you can support your liver’s function and potentially improve your ALT levels. However, always consult with your healthcare provider before making significant changes to your diet or exercise routine, especially if you have existing liver conditions.

Advanced Diagnostic Techniques: Beyond ALT Testing

While ALT testing is a valuable tool for assessing liver health, there are cases where additional diagnostic techniques may be necessary to provide a more comprehensive evaluation of liver function and structure.

What advanced diagnostic methods complement ALT testing?

When ALT levels are persistently elevated or when more detailed information about liver health is required, healthcare providers may recommend:

• Liver ultrasound: A non-invasive imaging technique that can detect structural changes in the liver, such as fatty infiltration or tumors
• Computed tomography (CT) scan: Provides detailed cross-sectional images of the liver, helping to identify abnormalities not visible on ultrasound
• Magnetic resonance imaging (MRI): Offers high-resolution images of liver tissue and can be particularly useful in detecting certain liver conditions
• Fibroscan: A specialized ultrasound that measures liver stiffness, helping to assess the degree of liver fibrosis or cirrhosis
• Liver biopsy: An invasive procedure where a small sample of liver tissue is removed for microscopic examination, providing detailed information about liver cell health and potential disease processes

These advanced diagnostic techniques, when used in conjunction with ALT and other liver function tests, allow for a more precise diagnosis and tailored treatment approach for various liver conditions.

When are advanced diagnostic techniques necessary?

Advanced liver diagnostics may be recommended in the following scenarios:

• Persistently elevated ALT levels without a clear cause
• Suspected advanced liver disease or cirrhosis
• Evaluation of liver tumors or masses
• Assessment of liver damage progression in chronic liver diseases
• Monitoring response to treatment in liver conditions
• Pre-transplant evaluation for liver transplant candidates

The decision to pursue advanced diagnostic techniques is based on individual patient factors, clinical presentation, and the results of initial liver function tests, including ALT levels.

ALT Testing in Special Populations: Considerations and Interpretations

While ALT testing is a standard component of liver health assessment, interpreting results can be more complex in certain populations. Understanding these nuances is crucial for accurate diagnosis and appropriate management.

How does ALT interpretation differ in special populations?

ALT levels and their interpretation may vary in:

• Pregnant women: ALT levels can be slightly elevated during normal pregnancy, particularly in the third trimester
• Children and adolescents: Normal ranges for ALT can differ from adult ranges and may vary with age and gender
• Elderly individuals: ALT levels tend to decrease with age, potentially masking liver disease in older adults
• Athletes: Intense exercise can temporarily elevate ALT levels, necessitating careful interpretation in physically active individuals
• Individuals with muscle disorders: Certain muscle conditions can lead to elevated ALT levels, complicating liver health assessment

Healthcare providers must consider these factors when interpreting ALT results in special populations to avoid misdiagnosis or unnecessary interventions. Additional testing or specialized reference ranges may be needed to ensure accurate assessment of liver health in these groups.

What additional considerations are necessary for ALT testing in special populations?

When conducting ALT testing in special populations, healthcare providers should:

• Use age and gender-specific reference ranges when appropriate
• Consider the timing of the test in relation to physical activity, especially in athletes
• Evaluate ALT levels in conjunction with other liver function tests and clinical symptoms
• Be aware of potential confounding factors, such as medications or underlying health conditions
• Consider repeat testing or additional diagnostic methods when results are ambiguous

By taking these factors into account, healthcare providers can ensure more accurate interpretation of ALT results and appropriate management of liver health across diverse patient populations.

Alanine transaminase (ALT) blood test

Medical Tests 

Definition

The alanine transaminase (ALT) blood test measures the level of the enzyme ALT in the blood.

Alternative Names

SGPT; Serum glutamate pyruvate transaminase; Alanine transaminase; Alanine aminotransferase

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

No special preparation is needed.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.

Why the Test is Performed

ALT is an enzyme found in a high level in the liver. An enzyme is a protein that causes a specific chemical change in the body.

Injury to the liver results in release of ALT into the blood.

This test is mainly done along with other tests (such as AST, ALP, and bilirubin) to diagnose and monitor liver disease.

Normal Results

The normal range is 4 to 36 U/L.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your health care provider about the meaning of your specific test results.

What Abnormal Results Mean

An increased ALT level is often a sign of liver disease. Liver disease is even more likely when the levels of substances checked by other liver blood tests have also increased.

An increased ALT level may be due to any of the following:

• Scarring of the liver (cirrhosis)
• Death of liver tissue
• Swollen and inflamed liver (hepatitis)
• Too much iron in the body (hemochromatosis)
• Too much fat in the liver (fatty liver)
• Lack of blood flow to the liver (liver ischemia)
• Liver tumor or cancer
• Use of drugs that are toxic to the liver
• Mononucleosis (“mono”)
• Swollen and inflamed pancreas (pancreatitis)

Risks

adam.com”>There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Multiple punctures to locate veins
• Hematoma (blood collecting under the skin)
• Infection (a slight risk any time the skin is broken)

References

Chernecky CC, Berger BJ. Alanine aminotransferase (ALT, alanine transaminase, SGPT) – serum. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:109-110.

Pincus MR, Tierno PM, Gleeson E, Bowne WB, Bluth MH. Evaluation of liver function. In: McPherson RA, Pincus MR, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 23rd ed. St Louis, MO: Elsevier; 2017:chap 21.

Pratt DS. Liver chemistry and function tests. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran’s Gastrointestinal and Liver Disease. 10th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 73.

Review Date: 01/26/2019

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only — they do not constitute endorsements of those other sites. Copyright ©2019 A.D.A.M., Inc., as modified by University of California San Francisco. Any duplication or distribution of the information contained herein is strictly prohibited.

Information developed by A.D.A.M., Inc. regarding tests and test results may not directly correspond with information provided by UCSF Health. Please discuss with your doctor any questions or concerns you may have.

Alanine Aminotransferase (ALT) Test and Results (aka SGPT Test)

Written by WebMD Editorial Contributors

• Why Is ALT Important?
• Why Would My Doctor Order This Test?
• How Do I Prepare?
• What Happens During the Test?
• What Are the Risks?
• What Do the Results Mean?
• What Other Tests Will I Take?
• More

The alanine aminotransferase (ALT) test is a blood test that checks for liver damage. Your doctor can use this test to find out if a disease, drug, or injury has damaged your liver.

Your liver does a lot of important things for you:

• It makes a fluid called bile that helps your body digest food.
• It removes waste products and other toxins from your blood.
• It produces proteins and cholesterol.

Diseases such as hepatitis and cirrhosis can damage your liver and prevent it from doing its many jobs.

This enzyme is found mainly in your liver. Smaller amounts of ALT are in your muscle, kidneys , and other organs.

Your body uses ALT to break down food into energy. Normally, ALT levels in the blood are low. If your liver is damaged, it will release more ALT into your blood and levels will rise. (ALT used to be called serum glutamic-pyruvic transaminase, or SGPT).

Doctors often give the ALT test along with other liver tests.

Your doctor might recommend ALT if you have symptoms of liver disease or damage, such as:

• Stomach pain or swelling
• Nausea
• Vomiting
• Yellow skin or eyes (a condition called jaundice)
• Weakness
• Extreme tiredness (fatigue)
• Dark-colored urine
• Light-colored poop
• Itchy skin

Here are some reasons you might get this test:

• You’ve been exposed to the hepatitis virus.
• You drink a lot of alcohol.
• You have a family history of liver disease.
• You take medicine that’s known to cause liver damage.

The ALT test can be done as part of a blood panel during a regular exam. If you’ve already been diagnosed with liver disease, your doctor can use the ALT test to see how well your treatment is working.

You don’t need any special preparation for the ALT test. Your doctor might ask you to stop eating or drinking a few hours before the test.

Tell your doctor what prescription drugs or supplements you take. Some medicines can affect the results of this test.

A nurse or lab tech will take a sample of your blood, usually from a vein in your arm. They will first tie a band around the upper part of your arm to make your vein fill with blood and swell up. Then they will clean the area with an antiseptic and place a needle into your vein. Your blood will collect into a vial or tube.

The blood test should take only a couple of minutes. After your blood is taken, the lab tech will remove the needle and band, then put a piece of gauze and a bandage over the spot the needle went in to stop the bleeding.

The ALT blood test is safe. Risks are usually minor, and can include:

• Bleeding
• Bruising
• Infection
• Slight pain when the needle is inserted
• Fainting or feeling dizzy

You should get your results in about a day. A normal ALT test result can range from 7 to 55 units per liter (U/L), but it varies depending on the laboratory used. Levels are normally higher in men.

Slightly high ALT levels may be caused by:

• Alcohol abuse
• Cirrhosis (long-term damage and scarring of the liver)
• Mononucleosis
• Drugs such as statins, aspirin, and some sleep aids

Moderately high ALT levels may be because of:

• Chronic (ongoing) liver disease
• Alcohol abuse
• Cirrhosis
• Blockage of the bile ducts
• Heart attack or heart failure (when your heart can’t pump enough blood to your body)
• Kidney damage
• Muscle injury
• Damage to red blood cells
• Heat stroke
• Too much vitamin A

Very high ALT levels can be caused by:

• Acute viral hepatitis
• An overdose of drugs such as acetaminophen (Tylenol)
• Liver cancer
• Sepsis

ALT usually is done as part of a group of liver function tests called a liver panel.

This panel also includes an aspartate aminotransferase (AST) test. AST is another liver enzyme. As with ALT, the levels of AST in your blood rise if your liver is damaged.

Comparing ALT with AST levels gives your doctor more information about the health of your liver. The AST-to-ASL ratio can help your doctor figure out how severe the liver damage is and what might have caused it.

To find out what type of liver disease you have, your doctor might also test the levels of other enzymes and proteins found in your liver, including:

• Albumin
• Alkaline phosphatase
• Bilirubin
• Lactate dehydrogenase (LDH)
• Total protein
• GGT

Talk to your doctor to make sure you understand all of your liver test results. Also find out how these results might affect your treatment.

Top Picks

ALT (ALT, Alanine aminotransferase, alanine transaminase, SGPT, Alanine aminotransferase)

Alanine aminotransferase (AlAT, ALT) is an intracellular enzyme, the content of which in the blood of healthy people is low. It is mainly found in the cells of the liver, myocardium, skeletal muscles, pancreas. When cells containing ALT are damaged or destroyed, the enzyme is released into the bloodstream, and its concentration in the blood increases.

Determination of the level of alanine aminotransferase is carried out for the diagnosis of liver diseases and dynamic monitoring of their treatment. The analysis is performed for suspected acute or chronic hepatitis of viral or toxic etiology, cirrhosis of the liver, primary tumors, or metastatic liver disease.

The growth of alanine aminotransferase in the blood in hepatitis is noted much earlier than the onset of the icteric stage, which makes it possible to identify the pathology at the initial stage.

As part of a screening examination (preventive examination of persons who do not have complaints) to assess the condition of the liver, before planned hospitalization and surgical treatment, an analysis for ALT is prescribed together with another enzyme – AsAT (aspartate aminotransferase).

The level of ALT together with other enzymes is evaluated in diseases of the pancreas and gallbladder – pancreatitis, cholecystitis, cholelithiasis; if there are complaints of unexplained general weakness, fatigue, yellowness of the skin and sclera, abdominal pain, including a feeling of heaviness in the right hypochondrium, nausea, vomiting.

In addition, the ALT level is taken into account in myocardial infarction and myocarditis, although in cases of heart damage it is only of secondary importance. The study is prescribed for suspected myositis, myodystrophy, when complaints of muscle pain cannot be explained by injuries or excessive physical activity.

Donation is a mandatory reason for testing for ALT.

ALT values ​​are assessed in any chronic disease, before prescribing drug therapy, for example, antitumor, anti-tuberculosis drugs, to assess the initial state of the liver and over time to assess drug tolerance.

Preparation for procedure

It is better to take the test in the morning on an empty stomach (after an 8-14 hour break after the last meal).

Drinking water is allowed.

If necessary, it is permissible to donate blood 4-6 hours after a light meal.

On the eve it is desirable to avoid physical and emotional overload, overeating.

Avoid drinking alcohol 5-6 days before the test.

Avoid smoking 30 minutes before blood sampling.

Deadline

The survey is completed within one business day.

What can affect the results

Intense physical activity the day before and even a few days before the test can lead to damage to muscle tissue (the so-called tear of muscle fibers) and, accordingly, an increase in the level of ALT. For the same reason, the analysis given after the injury is not informative.

Taking alcohol, certain drugs (antibiotics, non-steroidal anti-inflammatory drugs, anticancer drugs, oral contraceptives, etc.) often distort the result of the study. The list of medications taken should be discussed with the doctor who ordered the analysis, cancel those that are possible – without risk to health.

ALT (ALT, Alanine aminotransferase, alanine transaminase)

For research, blood is taken from a vein. Usually, ASAT (AST, Aspartate aminotransferase) is determined simultaneously and the ratio of ASAT / AlAT (de Ritis coefficient) is estimated.

You can take a blood test for ALT (ALT, Alanine aminotransferase, alanine transaminase) at the nearest INVITRO medical office. The list of offices where biomaterial is accepted for laboratory testing is presented in the “Addresses” section.

Interpretation of test results contains information for the attending physician and is not a diagnosis. The information in this section should not be used for self-diagnosis or self-treatment. An accurate diagnosis is made by the doctor, using both the results of this examination and the necessary information from other sources: history, results of other examinations, etc.

Normal

Units of measure: U/l.

Reference values ​​

Explanation of indicators

The level of ALT depends on the age and sex of the patient. Minor deviations from the norm, as a rule, do not require drug therapy, and the recommendations associated with them, such as rational nutrition, avoidance of alcohol, etc. should be discussed with your doctor.

The AST/ALAT ratio (de Ritis ratio) is normally between 0.91 and 1.75.

What do low values ​​mean

A significant decrease in the level of ALT can be detected in severe liver damage, for example, in the terminal stage of liver cirrhosis, when the number of liver cells is significantly reduced.

What do increased indicators mean

First of all, with an increase in ALT, liver problems should be suspected: fatty hepatosis, hepatitis of viral or toxic etiology, cirrhosis of the liver, liver cancer – primary or metastatic.

The degree of increase in ALT is usually associated with the extent or severity of liver damage, but cannot be considered as a determining factor for the prognosis of the disease. The maximum levels of ALT (and AST) – more than a hundred times higher than the norm, are observed in patients with acute viral and drug-induced hepatitis.

A significant increase in alanine aminotransferase can be observed in acute cholecystitis, cholelithiasis, and acute destructive pancreatitis. Another reason may be the use of hepatotoxic drugs that damage liver cells.

An increase in the level of ALT is detected with extensive injuries of the skeletal muscles, severe myositis and myodystrophy, frequent intramuscular injections.

A less significant increase in ALT is recorded in acute myocardial infarction and myocarditis.

Additional examination in case of deviation of the indicator from the norm

If a change (often an increase) in the level of ALT is detected, patients are consulted

general practitioners

,

gastroenterologists

, hepatologists, infectious disease specialists.

To clarify the diagnosis, in addition to ALT, other liver enzymes (AST, gamma-HT, alkaline phosphatase, bilirubin), clinical blood counts, and markers of viral hepatitis, primarily hepatitis B and hepatitis C, are usually examined.

An ultrasound examination of the abdominal organs is performed, according to indications – computed tomography (CT) with contrast.

If damage to the skeletal muscles is suspected, the CPK enzyme is additionally examined and a rheumatologist is consulted.

If a heart muscle disorder is suspected, a cardiologist should be consulted. Usually, the doctor prescribes additional electrocardiography (ECG), echocardiography, blood test for CF-CF, troponin I.

The role of new reference values ​​of alanine aminotransferase in the diagnosis of various forms of non-alcoholic fatty liver disease in patients with metabolic syndrome. Journal of Biomedical Technologies № 1. 2015. P. 9-15.

Clinical guidelines “Liver cancer (hepatocellular)”. Developed by: Association of Oncologists of Russia, Russian Society of Clinical Oncology, Russian Society of Radiologists and Radiologists. – 2020.

IMPORTANT!

The information in this section should not be used for self-diagnosis or self-treatment. In case of pain or other exacerbation of the disease, only the attending physician should prescribe diagnostic tests. For diagnosis and proper treatment, you should contact your doctor.
For a correct assessment of the results of your analyzes in dynamics, it is preferable to do studies in the same laboratory, since different laboratories may use different research methods and units of measurement to perform the same analyzes.

Test norms. Analysis decoding. Reference values, interval. “Norm” and “pathology” in laboratory diagnostics.

This article describes what test norms are, how tests are deciphered, why it is not modern to say “norm”, and what are reference values ​​​​and reference intervals.

Standards for interpretation of analyzes. Concept of reference values ​​and reference interval.

Information obtained in the course of laboratory analysis is based on the detection and / or measurement in clinical samples (biomaterial) of patients of certain components – analytes, functionally or structurally related to a particular organ or system of human organs. The most important component of any laboratory research is the interpretation of its result. Establishing the difference between the norm of analyzes and pathology plays a key role in assessing the data obtained. In practice, this is not difficult to do with a clear deviation of laboratory parameters from the values ​​taken as the norm. However, it is not always easy to divide most of the results of laboratory tests into “normal” and “pathology”, and therefore, in order to interpret them, a comparison of the data obtained with the indicators established as the norm is required.

Normal test values ​​(norm) are values ​​found in healthy people. However, in the groups of the latter, they can have different values, that is, the norm is individual. This is due both to the individual physiological characteristics of the human body (characteristics of metabolism, circadian biological rhythms, the functional state of certain organs and their systems), and differences in gender, age, and physiological state. For example, during pregnancy, many biochemical parameters of a woman’s body change, therefore, appropriate individual norms are determined for pregnant women.

Normal laboratory values ​​are determined in experimental clinical studies based on the results of measurements of the analyte under investigation in a large population of healthy people, specially selected and grouped by age, sex or other biological and other factors. The data obtained lead to the mean value, taking into account the statistically possible standard deviations of its value. In this regard, it is more correct to speak not about the “norm” of a laboratory indicator, but about the range in which normal (reference) values ​​are located. Therefore, at present, the term “norm”, which has already become familiar in assessing the results of a laboratory study, is used less often. Instead, they talk about reference (reference) values ​​ and the results obtained for a particular patient are compared with the so-called reference interval (range) . This term is more accurate, because it gives an idea of ​​the lower and upper limits of the norm of a laboratory indicator, possible, statistically significant limits of fluctuation (deviation) of its value and, at the same time, emphasizes the relativity of these data, the possibility of applying only to a certain group of people.

Explanation of analyzes. Norm or pathology?

When establishing the reference range, mathematical and statistical approaches are used, according to which the values ​​of the results of laboratory studies of a certain analyte of 95% of healthy people fall within the established interval. Accordingly, for 5% – the values ​​of the analyzed indicators are outside the established range. In other words, in 5% of cases in healthy people, “abnormal” laboratory parameters are detected, which should be taken into account when deciphering the analysis. This is explained by a number of reasons.

Firstly, the division of the biological population of people into “sick” and “healthy” according to many laboratory parameters is very conditional. Being statistical data, the limits of normal laboratory values ​​may vary. Therefore, it happens that in healthy people certain indicators that are “normal” for them are not ultimately “normal” for most others, and therefore do not fall into the range of generally accepted reference values. In this case, the limits of the reference range cannot serve as absolute indicators of health or disease.

On the other hand, often the disease develops imperceptibly, manifesting itself as a gradual transition from small deviations in the values ​​of laboratory parameters to their higher values ​​as dysfunction increases and the severity of the disease progresses. In this regard, when deciphering the analyzes in interpreting the results of laboratory tests, it becomes very important for the clinician to assess the dynamics of changes in a particular laboratory indicator in a particular patient. In doubtful cases, the main criterion for the presence or absence of a disease is the clinical symptomatology or the degree of its severity. In the presence of symptoms of the disease, additional laboratory tests are used for diagnosis using highly sensitive and specific tests that most pronouncedly change their values ​​against the background of the suspected disease.

Secondly, “healthy” and “sick” people actually belong to two different populations, and when these populations are mixed with each other, it is almost impossible to recognize each of them in the total mass. In addition, in different patients, the same indicator can not only take on different values, but also overlap the values ​​of this indicator in healthy people. Moreover, for different indicators, different diseases, different groups of patients, the value of such a “crossover” can vary greatly: from too small, which can be neglected, to very significant, when a special approach and careful analysis of all data is required to classify the result as “normal” or “pathological”. The latter is extremely important to take into account when evaluating the results of laboratory tests, since in this case not all values ​​that are outside the normal range will indicate the presence of pathology. The range of values ​​in which the laboratory parameters of “sick” and “healthy” individuals overlap is called the zone of uncertainty, or the “gray zone”. It exists for a range of laboratory procedures, but is most commonly found in enzyme immunoassay results. If the result falls into the “gray zone”, it cannot be unequivocally regarded either as a norm or as a pathology and is considered as doubtful. In such a case, the patient is usually advised to repeat the diagnostic study 2 to 4 weeks after receiving an indeterminate result.

And, finally, not always an indicator lying in the reference interval can be considered normal, since the range of many of them is quite wide. For example, the normal value of hematocrit (Ht) in men varies from 42 to 52%. Massive blood loss can lead to a drop in this indicator from 52 to 42%, while the value of 42% remains within the range of reference values, and therefore may not cause alarm for doctors. However, in a certain situation, for a particular patient, such a decrease in hematocrit can be not only clinically significant, but also critical.

Therefore, results within the reference range are not always normal. And, on the contrary, the results that go beyond the reference values ​​are not always pathology, but only a significant prognostic sign that can signal a possible pathological process. In this regard, in laboratory diagnostics, the approach is becoming more widespread, when the most significant and adequate reference values ​​for each individual patient should be considered stable results of his laboratory studies obtained over several years. Already at present, experts around the world are inclined to believe that it is necessary to “lower” the significance of reference intervals, moving away from interpreting them as some kind of “absolute” criterion for evaluating a laboratory result. This circumstance in no way reduces the importance of laboratory research. They remain the most important tool for diagnosing pathological conditions, monitoring the course of diseases, identifying the preclinical stage of diseases during screening examinations, and also largely determine the further tactics of diagnostic procedures and treatment decisions. However, this approach directs the clinician to more cautious use of reference values ​​in the assessment of “normal” and “pathological” results, indicating the need for their interpretation, taking into account possible biological variation in the population, taking into account the data of the clinical picture and other types of studies in the aggregate, as well as those factors that may influence the results of laboratory studies.

Reference ranges

Reference values ​​have now been established for many laboratory parameters. The results of some types of research are given to the patient in the form of “yes” or “no”. This type of research is qualitative. For example, a positive result for antibodies to a specific infection indicates the presence of these antibodies in the patient’s blood and may indicate infection. In the case when the study was quantitative, the result is issued as a numerical value, indicating on the form the units of measurement and the corresponding reference range. For example, the results of a biochemical study to determine the level of C-reactive protein (CRP), which is a marker of inflammation, may look like this: 0.4 mg / l, reference values: 0 – 6 mg / l. From the above example, it can be seen that the result obtained is within the established reference range. For most laboratory parameters, the range of reference values ​​is indicated taking into account the patient’s gender and / or his belonging to a certain age group. For example, the reference values ​​​​of serum creatinine for children under 1 year old are 18 – 35 µmol / l, for children from one to 14 years old – 27 – 62 µmol / l, and for people over 14 years old – 62 – 115 µmol / l for males and 53 – 97 µmol/l for females.

The effect of age and gender on the range of reference values ​​is significant for many laboratory tests. For example, the concentration of alkaline phosphatase, a key enzyme secreted by bone tissue cells, increases in proportion to the rate of formation of new bone cells. Therefore, in children and adolescents, a high level of this enzyme is not only normal, but also desirable, since it is associated with the active formation and growth of bones. On the contrary, a high level of alkaline phosphatase in an adult may indicate developing osteoporosis, metastases of bone tumors, or other pathological processes. The exception is pregnant women, who are characterized by a physiological increase in the activity of this enzyme, especially in the third trimester of pregnancy.

Why can reference ranges vary from laboratory to laboratory?

Different diagnostic laboratories use different types of laboratory equipment to perform analysis, for example, biochemical and immunochemical analyzers, the range of which is currently very wide, work on reagents from different manufacturers, and in addition, they may use different research methods than other laboratories. In this regard, each laboratory indicates on the form of results its ranges of reference values, when establishing which, of course, it is guided by generally accepted standards, but taking into account the individual characteristics of its work: the specifics of the equipment used, the methods of analysis used and units of measurement. That is why the ranges of reference values ​​for the same laboratory test may vary according to the data of different diagnostic laboratories, and there is no such thing as a “single” reference range. When evaluating the results of laboratory tests, the attending physician should first of all refer to the range of reference values ​​indicated on the form of the laboratory in which the analysis was performed. In order for the results to be interpreted correctly and comparable, especially in the case of repeated studies, for example, when monitoring therapy or dynamic assessment of the patient’s condition, it is advisable to conduct studies using the same method, in the same laboratory and, if possible, other things being equal.

Factors affecting laboratory results

Modern methods of clinical laboratory research are characterized by high sensitivity and specificity, and therefore their results, reflecting the patient’s health status, can serve as the basis for making important clinical decisions by the attending physician. At the same time, both clinicians and patients should understand that there are a number of non-pathological factors that can, to a certain extent, influence the results of laboratory tests, distorting the objective picture of the patient’s health. Some of these factors can only be controlled by the efforts of laboratory specialists, minimizing their possible negative impact on the final result of the laboratory study. Among such factors, for example, the conditions and method of taking biological material, delivery and storage of samples, the correctness of their identification in the laboratory. However, to minimize the negative impact of many other factors that affect the accuracy of the final result of a laboratory test, only the patient himself or his attending physician, who must inform the patient about the correct preparation for a certain type of laboratory test, can. Compliance with the doctor’s instructions will allow the analysis to be as close as possible to the general requirements, for example, the need to donate blood on an empty stomach, and thereby bring the results of the study as close as possible to the reference ones for this group of patients.

What factors can influence the results of laboratory tests? First of all, it should be noted the sensitivity of many laboratory tests to the time interval associated with the patient’s intake of food in general or individual products in particular, as well as the peculiarities of his eating behavior, for example, diet (meat or vegetarian), coffee and alcohol consumption. For example, high blood sugar may be related to a recent meal rather than diabetes. Eating shortly before the study will affect the results of lipid profile tests, insulin and C-peptide levels. In this regard, in order to obtain accurate results of the study, it is recommended to donate blood in the morning on an empty stomach, usually not less than 8 and not more than 14 hours after the last meal. On the eve of the study, food overload should be avoided.

High levels of liver enzymes may be due to recent or frequent alcohol use. Caffeine can cause an increase in the concentration of catecholamines and renin in plasma. Smoking sometimes causes a borderline increase in the level of some tumor markers.

Lab test results may be affected by vitamin and nutritional supplements and medications. In this case, the effect of drugs can be multidirectional. They can not only change the physiological processes in the body, but also chemically interfere (interact) with the analyzed analyte under conditions in vitro . An example of the effect of drugs on the physiological level is the increase in liver enzymes under the influence of hepatotoxic drugs. Drugs that affect plasma volume can cause changes in the concentration of proteins, urea nitrogen, iron and calcium. An example of another influence is non-specific binding reactions of certain drug metabolites with individual components of the reaction mixture, for example, polyclonal antibodies in immunoassays, as a result of which an erroneous result can be obtained. In this regard, a patient taking any medications should consult with a doctor about the advisability of conducting a laboratory study while taking medications or the possibility of stopping them before the study.

Among the factors affecting the results of laboratory tests is physical activity. Physical stress leads to a volumetric shift between the vascular bed and the intercellular space, loss of fluid with sweat and, as a result, to a change in the concentration of some analytes: hormones or enzymes. Therefore, visiting, for example, a gym on the eve of a laboratory test is undesirable. Heavy physical activity can cause an increase in the level of certain enzymes (ALT, AST, LDH, creatine kinase), a change in the level of various blood substrates (glucose, urea, etc.), and increase the excretion of protein in the urine. In addition, people who have been actively involved in sports for a long time, such as long-distance running or weightlifting, may have slightly increased levels of testosterone and luteinizing hormone (LH).

A general recommendation to prepare for the test is to rest (preferably sit) for 10 to 20 minutes after arriving at the laboratory before taking blood samples. This is also due to the fact that the results of some laboratory tests can be influenced by the body position of the subject at the time of its conduct, as well as the emotional state of the person before and during the study. So, for example, a change in body position from a lying position to a sitting or standing position causes vasoconstriction, and a change in position from a sitting to a lying position causes a shift of water and electrolytes in the tissue, leading to blood concentration. As a result, serum or plasma levels of total protein, albumin, lipids, iron and calcium change upward.

Emotional stress can cause significant increases in cortisol, ACTH and glucose levels. Among other things, stress is combined with an increase in the concentrations of albumin, fibrinogen, insulin, lactate and cholesterol. That is why it is so important, if possible, to exclude psycho-emotional stress on the eve of the study and try not to worry in the process of taking a biological sample.

Temporary changes in some laboratory parameters may be caused by physiotherapy and instrumental examinations (eg, prostate biopsy before PSA testing). In such cases, it is recommended to postpone the laboratory examination for several days.

For a number of hormonal studies, it is important to take into account the phase of the menstrual cycle in women, and therefore it is necessary to check with the doctor in advance the optimal days for blood donation to determine the level of FSH, LH, inhibin B, prolactin, progesterone, estradiol and some other hormones.

Time of day during sampling is particularly important when cortisol, thyroid stimulating hormone (TSH), and some other analytes are needed. At the same time, it should be borne in mind that the reference values ​​- the boundaries of the “normal” laboratory parameters, usually reflect the statistical data obtained under standard conditions when taking blood in the morning.

Thus, there are a number of reasons why the results of the analysis may fall outside the established range of reference values, even if the person is absolutely healthy. Therefore, if the patient is aware of any special circumstances that could affect the results of the studies, they should be reported to their doctor. Don’t expect him to figure them out on his own. After all, a result that does not correspond to the “norm” is not necessarily a sign of a disease, and therefore the doctor needs to understand its possible cause. It is possible that this is just the case when the result obtained falls into those very statistically significant 5%, in which the laboratory parameters of healthy people are outside the reference range. Sometimes some “abnormal” results can go back to normal on their own, especially if they were on the border of the reference values. In addition, there are not many diseases that can be diagnosed with just one single test.

The above examples show that in order to adequately evaluate the results of laboratory tests, as well as to make the right clinical decisions for the patient on the basis of them, a comprehensive approach is needed that takes into account all the variety of factors that can affect the accuracy and correctness of the data obtained. Clinical conclusions and decisions based on the results of laboratory analyzes will be correct only if the various preanalytical and analytical factors are sufficiently standardized and fully taken into account. It is very important that the patient is able to follow all the necessary recommendations for preparing for laboratory tests, and the attending physician, interpreting the data obtained, would take into account the possible impact on the result of the study of non-pathological factors that occurred, and also comprehensively evaluate the results, taking into account the clinical picture and data from other types of studies.

Laboratory diagnostics specialists, if necessary, are always ready to answer questions on the results obtained, provide additional special information and explanations or consult in complex cases.

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