C Reactive Protein – StatPearls

Sara M. Nehring; Amandeep Goyal; Bhupendra C. Patel.

Author Information and Affiliations

Last Update: July 18, 2022.

Introduction

C-reactive protein (CRP) was discovered by Tillett and Francis in 1930. The name CRP arose because it was first identified as a substance in the serum of patients with acute inflammation that reacted with the “c” carbohydrate antigen of the capsule of pneumococcus.

CRP is a pentameric protein synthesized by the liver, whose level rises in response to inflammation. CRP is an acute-phase reactant protein that is primarily induced by the IL-6 action on the gene responsible for the transcription of CRP during the acute phase of an inflammatory/infectious process. There is some question about whether dysregulation of the role of CRP in the clearance of apoptotic cells and cellular debris plays a role in the pathogenesis of systemic lupus erythematosus (SLE), but this has not been definitively demonstrated. It has been demonstrated to have some protective properties in animal studies on lung tissue in alveolitis by reducing neutrophil-mediated damage to the alveoli and protein leakage into the lung.

CRP has both proinflammatory and anti-inflammatory properties. It plays a role in the recognition and clearance of foreign pathogens and damaged cells by binding to phosphocholine, phospholipids, histone, chromatin, and fibronectin. It can activate the classic complement pathway and also activate phagocytic cells via Fc receptors to expedite the removal of cellular debris and damaged or apoptotic cells and foreign pathogens. This can become pathologic, however, when it is activated by autoantibodies displaying the phosphocholine arm in auto-immune processes, such as idiopathic thrombocytopenic purpura (ITP). It can also worsen tissue damage in certain cases by activation of the complement system and thus inflammatory cytokines.[1][2][3]

As compared to the erythrocyte sedimentation rate, which is an indirect test for inflammation, the levels of CRP rise and fall rapidly with the onset and removal of the inflammatory stimulus, respectively. Persistently elevated CRP levels can be seen in chronic inflammatory conditions such as chronic infections or inflammatory arthritides such as rheumatoid arthritis.

There are numerous causes of an elevated C-reactive protein.  These include acute and chronic conditions, and these can be infectious or non-infectious in etiology. However, markedly elevated levels of CRP are most often associated with an infectious cause[4] (an example of pathogen-associated molecular pattern recognition).  Trauma can also cause elevations in CRP (alarmin response). More modest elevations tend to be associated with a broader spectrum of etiologies, ranging from sleep disturbances to periodontal disease.

Specimen Collection

A blood specimen is taken from a peripheral venous draw. A phlebotomist performs the procedure in most cases. The phlebotomist secures a snug rubber band around the upper arm, and the patient pumps his or her fist several times. The phlebotomist palpates the vein to confirm the location and cleanses the area with an alcohol prep pad. Once the area air dries, the practitioner introduces a needle into the vein and draws a vial of blood. He or she removes the band from the patient’s arm and then removes the needle and applies pressure to the venipuncture site until hemostasis occurs, usually within one minute. A bandage is applied over the site.

The patient’s medications should be reviewed, as these can affect the outcome of the test. Fasting is not required before the blood draw. There are no special procedures required. Complications include oozing at the draw site, bruising or mild tenderness at the site, or very rarely, infection at the venipuncture site. Other bodily fluids, such as synovial fluid, can be tested for in this manner but frequently are not.

Immunoassays and laser nephelometry are the methods to quantify CRP levels and are cheap, accurate, and fast. To detect lower levels of CRP (0.3 to 1.0 mg/L), high-sensitivity CRP methods are recommended as the usual CRP detection tests are less precise.  High-sensitivity CRP only denotes the assay process used, allowing for detection of lower levels of CRP and not a different, or more specific, differential diagnosis.

Indications

This test is performed when the physician suspects acute or chronic inflammation (e.g., SLE or rheumatoid arthritis [RA]) or infection. The utility of the hs-CRP for cardiac screening is debatable. There is some correlation between cardiovascular risk and elevated hs-CRP, but the application of this is still controversial especially given the poor specificity of this test, and it is currently undergoing more evaluation.[5][6][7]

Normal and Critical Findings

Lab values vary, and there is no standard at present.  However, in general, the result is reported in either mg/dL or mg/L. Hs-CRP is usually reported in mg/dL. When used for cardiac risk stratification, hs-CRP levels less than 1 mg/dL are considered low risk. Levels between 1 mg/dL and 3 mg/dL are considered a moderate risk, and a level greater than 3 mg/dL is considered high risk for the development of cardiovascular disease. [8][9] 

Interpretation of CRP levels:

Less than 0.3 mg/dL: Normal (level seen in most healthy adults).

0.3 to 1.0 mg/dL: Normal or minor elevation (can be seen in obesity, pregnancy, depression, diabetes, common cold, gingivitis, periodontitis, sedentary lifestyle, cigarette smoking, and genetic polymorphisms).

1.0 to 10.0 mg/dL: Moderate elevation (Systemic inflammation such as RA, SLE, or other autoimmune diseases, malignancies, myocardial infarction, pancreatitis, bronchitis).

More than 10.0 mg/dL: Marked elevation (Acute bacterial infections, viral infections, systemic vasculitis, major trauma).

More than 50.0 mg/dL: Severe elevation (Acute bacterial infections).

Interfering Factors

Certain medications, such as non-steroidal anti-inflammatory drugs (NSAIDs), will falsely decrease CRP levels. Statins, as well, have been known to reduce CRP levels falsely. Recent injury or illness can falsely elevate levels, particularly when using this test for cardiac risk stratification. Magnesium supplementation also can decrease CRP levels.

As mentioned above, mild elevations in CRP can be seen without any systemic or inflammatory disease. Females and elderly patients have higher levels of CRP. Obesity, insomnia, depression, smoking, and diabetes can all contribute to mild elevations in CRP, and the results shall be interpreted with caution in individuals with these comorbidities.

Complications

Given the highly variable causality of elevated CRP, marginal elevations in the CRP can be difficult to interpret and should not be used as an isolated test result interpreted as appropriate for the clinical picture. It is useful in suggesting infection versus inflammation if the levels are extremely high, but levels between 1 mg/dL and 10 mg/dL can be difficult to interpret accurately. Chronic conditions, such as inflammatory arthritis or SLE, can make these levels elevated chronically, making it harder to determine if there is any significance to an elevated hs-CRP level when using it as a predictive marker for cardiovascular disease.

Clinical Significance

Very high levels of CRP, greater than 50 mg/dL, are associated with bacterial infections about 90% of the time. In multiple studies, CRP has been used as a prognostic factor in acute and chronic infections, including hepatitis C, dengue, and malaria. [10][11][12] On the other hand, mild elevations may or may not be clinically relevant. Clinical correlation is strongly recommended while interpreting the results of the CRP test.

Review Questions

• Access free multiple choice questions on this topic.

• Comment on this article.

References

1.

Cleland DA, Eranki AP. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Aug 8, 2022. Procalcitonin. [PubMed: 30969616]

2.

Jungen MJ, Ter Meulen BC, van Osch T, Weinstein HC, Ostelo RWJG. Inflammatory biomarkers in patients with sciatica: a systematic review. BMC Musculoskelet Disord. 2019 Apr 09;20(1):156. [PMC free article: PMC6456959] [PubMed: 30967132]

3.

Kramer NE, Cosgrove VE, Dunlap K, Subramaniapillai M, McIntyre RS, Suppes T. A clinical model for identifying an inflammatory phenotype in mood disorders. J Psychiatr Res. 2019 Jun;113:148-158. [PubMed: 30954775]

4.

Vanderschueren S, Deeren D, Knockaert DC, Bobbaers H, Bossuyt X, Peetermans W. Extremely elevated C-reactive protein. Eur J Intern Med. 2006 Oct;17(6):430-3. [PubMed: 16962952]

5.

Eschborn S, Weitkamp JH. Procalcitonin versus C-reactive protein: review of kinetics and performance for diagnosis of neonatal sepsis. J Perinatol. 2019 Jul;39(7):893-903. [PubMed: 30926891]

6.

Darooghegi Mofrad M, Milajerdi A, Koohdani F, Surkan PJ, Azadbakht L. Garlic Supplementation Reduces Circulating C-reactive Protein, Tumor Necrosis Factor, and Interleukin-6 in Adults: A Systematic Review and Meta-analysis of Randomized Controlled Trials. J Nutr. 2019 Apr 01;149(4):605-618. [PubMed: 30949665]

7.

Dick AG, Magill N, White TCH, Kokkinakis M, Norman-Taylor F. C-reactive protein: what to expect after bony hip surgery for nonambulatory children and adolescents with cerebral palsy. J Pediatr Orthop B. 2019 Jul;28(4):309-313. [PubMed: 30925527]

8.

Lee Y, McKechnie T, Doumouras AG, Handler C, Eskicioglu C, Gmora S, Anvari M, Hong D. Diagnostic Value of C-Reactive Protein Levels in Postoperative Infectious Complications After Bariatric Surgery: a Systematic Review and Meta-Analysis. Obes Surg. 2019 Jul;29(7):2022-2029. [PubMed: 30895509]

9.

Johns I, Moschonas KE, Medina J, Ossei-Gerning N, Kassianos G, Halcox JP. Risk classification in primary prevention of CVD according to QRISK2 and JBS3 ‘heart age’, and prevalence of elevated high-sensitivity C reactive protein in the UK cohort of the EURIKA study. Open Heart. 2018;5(2):e000849. [PMC free article: PMC6269641] [PubMed: 30564373]

10.

Bhardwaj N, Ahmed MZ, Sharma S, Nayak A, Anvikar AR, Pande V. C-reactive protein as a prognostic marker of Plasmodiumfalciparum malaria severity. J Vector Borne Dis. 2019 Apr-Jun;56(2):122-126. [PubMed: 31397387]

11.

Vuong NL, Le Duyen HT, Lam PK, Tam DTH, Vinh Chau NV, Van Kinh N, Chanpheaktra N, Lum LCS, Pleités E, Jones NK, Simmons CP, Rosenberger K, Jaenisch T, Halleux C, Olliaro PL, Wills B, Yacoub S. C-reactive protein as a potential biomarker for disease progression in dengue: a multi-country observational study. BMC Med. 2020 Feb 17;18(1):35. [PMC free article: PMC7025413] [PubMed: 32063229]

12.

de Souza Pires-Neto O, da Silva Graça Amoras E, Queiroz MAF, Demachki S, da Silva Conde SR, Ishak R, Cayres-Vallinoto IMV, Vallinoto ACR. Hepatic TLR4, MBL and CRP gene expression levels are associated with chronic hepatitis C. Infect Genet Evol. 2020 Jun;80:104200. [PubMed: 31962161]

Disclosure: Sara Nehring declares no relevant financial relationships with ineligible companies.

Disclosure: Amandeep Goyal declares no relevant financial relationships with ineligible companies.

Disclosure: Bhupendra Patel declares no relevant financial relationships with ineligible companies.

High vs. Low Levels, Normal Range

Written by WebMD Editorial Contributors

Medically Reviewed by Jabeen Begum, MD on November 29, 2021

If you have high cholesterol, you’ve probably been told to lower the LDL number from your blood test. LDL is the “bad cholesterol,” the type that contributes to plaque that can clog your arteries. This can lead to a heart attack or stroke.

But that’s only part of the story. Research shows that only 50% of people who suffered heart attacks had high LDL levels. So, many doctors use another test called the C-reactive protein test to help figure out who’s at risk.

C-reactive protein (CRP) is produced by the liver. Its level rises when there is inflammation in your body. LDL cholesterol not only coats the walls of your arteries, but it also damages them. This damage causes inflammation that the body tries to heal by sending a “response team” of proteins called “acute phase reactants.” CRP is one of these proteins.

One study found that testing for CRP levels is a better indicator of cardiovascular disease (CVD) than the LDL test. But, it’s important to know that a CRP test is not a test for heart disease. It’s a test for inflammation in the body.

The test is also used for people suffering from autoimmune diseases like lupus and rheumatoid arthritis. They also cause inflammation. A doctor might test someone with either condition to see if anti-inflammatory medication is working, though the CRP test cannot determine where the inflammation is taking place.

A variation of the CRP test, the high-sensitivity CRP (hs-CRP), is used to check for cardiovascular disease.

It’s a simple blood test. A sample is drawn from a vein, most likely in your arm. No special preparation is needed (like fasting) and the test is not painful beyond a sting on the arm from where needle is inserted. The test may be affected by medications you take, so ask your doctor if you need to cut back beforehand. The blood sample is tested at a lab.

Here are what the results mean:

• hs-CRP level of lower than 1.0 mg/L — low risk of CVD (heart disease)
• hs-CRP level of 1.0 mg/L and 3.0 mg/L — moderate risk of CVD
• hs-CRP level of more than 3.0 mg/L — high risk of CVD

A high level could also be a sign of cancer, infection, inflammatory bowel disease, lupus, rheumatoid arthritis, tuberculosis, or another disease. It could also be high because you’re in the second half of your pregnancy or you are using birth control pills.

The hs-CRP test is most useful for people who have a 10%-20% chance of having a heart attack within the next 10 years. The test is not helpful for people with a higher or lower risk.

Because your CRP level can vary, the test should be done two times (2 weeks apart) to determine your risk of heart disease. It’s also important to remember that you could have a high reading without necessarily having heart disease. So, it’s important to check your LDL levels as well to get a full picture of your CVD risk.

Fortunately, the same statin medications that lower LDL have also been shown to lower CRP levels. In addition to any medicine, you should make some lifestyle changes (cut down on fatty foods, stop smoking, and start exercising) at the same time.

Top Picks

C-reactive protein (CRP, CRP), indications for the appointment, rules for preparing for the test, interpretation of the results and normal indicators.

I confirm

More

• INVITRO
• Library
• Laboratory…
• C-reactive protein…

Chicken pox

Rubella

Measles

Gout

Encephalitis

Hepatitis

Rheumatism

3007

06 October

We remind you that independent interpretation of the results is not allowed, the information below is for reference only.

C-reactive protein (CRP, CRP): indications for the appointment, rules for preparing for the test, interpretation of the results and normal indicators.

Indications for study appointment

C-reactive protein (CRP) is the most highly sensitive indicator of tissue damage during inflammation, necrosis, and trauma. In the blood of a healthy person, CRP is absent or detected in minimal amounts. It is produced mainly by liver cells (hepatocytes), as a reaction to infection pathogens entering the human body, to trauma, as well as in systemic connective tissue diseases (rheumatic diseases).

CRP stimulates immune reactions in the body, activates its defense systems and has a high correlation with the activity of the disease and the stage of the process, that is, its concentration becomes higher, the more active the inflammation (infectious or autoimmune) and the more extensive the area of ​​tissue damage during necrosis or trauma. Therefore, C-reactive protein is called the “acute phase” protein.

Another indicator of acute inflammation is the ESR (erythrocyte sedimentation rate).

ESR (Erythrocyte Sedimentation Rate, ESR)

ESR is a nonspecific marker of inflammation.

Synonyms: Erythrocyte sedimentation reaction; ROE.

Westergren sedimentation rate; Erythrocyte Sedimentation Rate; ESR; Sed Rate; sedimentation rate.

Red…

Up to 1 business day

Available with house call

295 RUB

Add to cart

However, CRP is more informative, since its level begins to rise earlier and decrease faster (with proper treatment, CRP decreases on days 6-10, while ESR only on days 14-28). In addition, the results of ESR are influenced by the gender of the patient (for women, the ESR is higher than for men), the time of day, the number of erythrocytes, and this does not affect the CRP values. Thus, for the assessment of the inflammatory process, the analysis for C-reactive protein seems to be more justified.

The level of CRP in viral diseases increases slightly, so its significant increase in combination with elevated body temperature most likely indicates the presence of a bacterial infection.

For a short time, C-reactive protein may increase after surgery due to tissue damage, but in the absence of bacterial inflammation in the postoperative period, it quickly decreases.

Whereas the addition of a bacterial infection, whether it is a local process or sepsis, is accompanied by an increase in CRP or the absence of its decrease.

There is a highly sensitive method for determining CRP – highly sensitive C-reactive protein (cardio). The study reveals an increase in CRP with a sluggish, low degree of inflammation of the inner surface of the vascular wall, which is fraught with the formation of atherosclerotic plaques. The analysis is prescribed only in the absence of acute diseases and injuries (in which an increase in CRP is detected by the standard method). An increase in the values ​​of highly sensitive C-reactive protein may indicate the risk of cardiovascular diseases: myocardial infarction, stroke.

Thus, an analysis for C-reactive protein in combination with the study of some indicators of a clinical blood test (leukocyte count, leukocyte count and ESR) is usually prescribed in case of an increase in body temperature in order to suggest viral or bacterial inflammation by the degree of their increase.

CRP is determined for pain in the joints, not associated with trauma, for the differential diagnosis of degenerative and inflammatory diseases – arthrosis and arthritis. In rheumatic diseases, CRP is examined to assess the activity of the process and monitor the effectiveness of treatment.

Preparing for the procedure

Donate blood preferably in the morning on an empty stomach, after an 8-14 hour break from eating. Do not drink juices, tea and coffee. Drinking water is allowed.

If necessary, CRP can be tested 4-6 hours after a light meal.

Physical activity should be avoided 2-3 days before the study.

Do not smoke for at least 30 minutes before blood sampling.

C-reactive protein (CRP, CRP)

C-reactive protein is an acute phase protein, a sensitive indicator of tissue damage during inflammation, necrosis, trauma.
Synonyms: Blood test for CRP; C-jet …

Up to 1 business day

Available with house call

665 RUB

Add to cart

Deadline

The analysis is carried out within one business day.

What can affect the results

A number of factors can influence the results of a study:

• Intense physical activity, which should be avoided 2-3 days before the test, as it can lead to damage to muscle tissue and, consequently, an increase in CRP. This is especially true for athletes and people who regularly visit gyms: any muscle injury leads to an increase in CRP levels.
• Non-steroidal anti-inflammatory drug (NSAID) painkillers and antipyretics may reduce actual CRP levels by reducing inflammation. There is evidence that statins used to lower blood cholesterol levels have a similar effect.
• The presence of implants and transplants in the body.
• Consumption of alcohol and/or fatty foods on the eve of the study.

C-reactive protein (CRP)

For research, blood is taken from a vein.

You can take a blood test for C-reactive protein (CRP, CRP) at the nearest INVITRO medical office. The list of offices where biomaterial is accepted for laboratory testing is presented in the “Addresses” section.

The interpretation of the results of the study 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 measurement: mg/l

A CRP level of less than 5 mg/l is considered normal.

When assessing cardiovascular risk, the level of highly sensitive CRP less than 1.0 mg/l is regarded as low, 1-3 mg/l as average, more than 3 mg/l indicates an increased risk of developing cardiovascular diseases in the future.

Explanation of indicators

The level of C-reactive protein in the blood does not depend on the gender and age of the patient, and its increase may be associated with damage to any organs and systems of the body of various nature. A specific diagnosis is established by a comprehensive assessment of complaints, examination data, instrumental and laboratory examination methods.

What do low readings mean

Since C-reactive protein is either absent in the blood of a healthy person, or is detected in minimal amounts, it is incorrect to talk about its decrease.

What do high rates mean

The degree of increase in C-reactive protein usually correlates with the volume, nature and severity of tissue damage.

An increase in CRP up to 30 mg/l can indicate viral diseases – SARS, rotavirus infection, etc., is found in malignant tumors, rheumatic diseases without an exacerbation stage (systemic lupus erythematosus, dermatomyositis, systemic scleroderma, rheumatoid arthritis, etc.).

An increase in CRP to 100 mg/l and above, as a rule, accompanies various acute bacterial infections (tonsillitis, pneumonia, appendicitis, acute cholecystitis, pyelonephritis, etc.), exacerbations of chronic infectious diseases and rheumatic diseases, as well as various tissue damage ( surgery, myocardial infarction, etc.).

The most significant increase in CRP – up to 300 mg / l or more is possible with extensive burns and sepsis, when bacteria from the lesion enter the bloodstream and spread throughout the body.

Additional examination in case of deviation from the norm

An increase in body temperature in combination with an increase in the level of C-reactive protein can be accompanied by generalized (common) and any local lesions – infections of the skin and subcutaneous adipose tissue, respiratory and dental infections, infections of the eyes, ENT organs, gastrointestinal tract, cardiovascular system, urological infections, infections of the central nervous system, bones and joints.

Depending on the clinical picture, such patients are examined and treated by doctors of different specialties – general practitioners, surgeons, narrow specialists, including ENT specialists, dentists, gynecologists, urologists, rheumatologists.

As additional research in each case, you may need a wide range of instrumental and laboratory diagnostics.

An increase in the level of highly sensitive CRP entails the identification of other risk factors for cardiovascular disease. For this, a blood test is performed for the lipid spectrum, fibrinogen, homocysteine, glucose, uric acid, as well as an ultrasound examination of the vessels of the neck and heart.

Sources

1. Ershov A.V. C-reactive protein in the diagnosis of community-acquired pneumonia. Consilium Medicum, magazine. 2019, 21(3): 15-19 p.
2. Khorolets E.V., et al. Diagnostic significance of C-reactive protein in the genesis of pathologies of the cardiovascular system. Journal of Fundamental Medicine and Biology. No. 1. 2013. S. 23-27.

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 can use different research methods and units of measurement to perform the same analyzes.

Recommendations

• PSA (prostate specific antigen) test

  385

  may 13

• Human papillomavirus

  5575

  04 May

• Alkaline phosphatase

  891

  16 April

Show more

Similar articles

Hemorrhoids

Fungus

Diarrhea

Gastritis

Hepatitis

Coprogram: what is this study?

Coprogram, general analysis of feces: indications for the appointment, rules for preparing for the delivery of the analysis, interpretation of the results and indicators of the norm.

More

Pyelonephritis

Hepatitis

Cystitis

Diabetes mellitus

Urinalysis (with sediment microscopy)

Urinalysis (with sediment microscopy): indications for appointment, rules for preparing for the test, interpretation of the results and normal indicators.

More

Hepatitis

Hepatitis C

Antibodies to hepatitis C virus class IgM and IgG (anti-HCV total)

Antibodies to hepatitis C virus class IgM and IgG (anti-HCV total): indications for prescription, rules for preparing for donation analysis, interpretation of the results and indicators of the norm.

More
Bio

Pyelonephritis

Hepatitis

Gout

Diabetes chemical blood test

Biochemical blood test: indications for prescription, rules for preparing for the test, interpretation of the results and norm indicators.

More

Atherosclerosis

Diabetes mellitus

Arthritis

Gout

Cholesterol

Cholesterol: indications for prescription, rules for preparing for the test, interpretation of the results and normal indicators.

More

Subscribe to our newsletters

Enter e-mail

I consent to

processing of personal data

Subscribe

norm, causes of deviations, what does it mean

Synonyms: CRP, CRP, C-reactive Protein

What it is

CRP is a blood plasma protein, the concentration of which increases during inflammation. Most of the protein is produced in liver cells in response to certain signals from macrophages (immune cells)¹.

The main function of SRP is protective. It activates the complement system (a group of proteins with antibacterial activity), as well as some cells of the immune system. The concentration of CRP increases in proportion to the scale of the inflammatory process. The more inflammation, the more protein is produced in the liver.

When inflammation becomes chronic, the level of CRP decreases (sometimes to zero). However, with exacerbations, it rises again.

Another property of CRP is the binding of low-density lipoprotein (LDL)². This is the so-called “bad cholesterol”. Thus, this protein contributes to the development of atherosclerosis. An increase in the concentration of C-reactive protein in the absence of acute infection or injury may indicate the risk of cardiac pathologies.

Blood test for C-reactive protein

Blood for determination of the level of C-reactive protein is taken from a vein. Photo: freepik.com

As a rule, C-reactive protein is determined in a biochemical blood test (CRP). The indicator is measured in milligrams per liter (mg / l). Blood for this analysis is taken from a vein.

Normal CRP values ​​may vary between laboratories. In most cases it is up to 1 mg/l. In some institutions – up to 5 mg / l. There is no lower limit for this marker, since the protein is determined in the acute phase of inflammation.

Indications

CRP in the blood is determined under the following circumstances:

• Symptoms of acute infectious diseases. These include high body temperature, headache, cough, urination disorders and others.
• As part of a comprehensive examination of healthy individuals, especially the older age group (over 45 years). This is done for preventive purposes.
• When examining patients with cardiovascular diseases (for example, coronary heart disease or arterial hypertension).
• Examinations in acute myocardial infarction.
• As part of a comprehensive assessment of people with chronic diseases such as diabetes mellitus, atherosclerosis or severe kidney problems. CRP in such people can determine the risk of cardiovascular complications.
• In control studies to evaluate the effectiveness of the treatment of cardiovascular pathologies. In particular, this is done when taking aspirin and statins in patients with atherosclerosis.
• Inflammatory processes of any origin. In addition to infectious pathologies, these are also parasitic, tumor diseases and injuries.
• Control tests to evaluate the effectiveness of antibiotic therapy for infectious diseases.

Preparation for analysis

No special preparation is required from the patient. It is necessary to comply with the standard requirements that apply before donating blood from a vein:

• You need to donate blood on an empty stomach, after 12-14 hours of fasting. As a rule, blood is taken in the morning. The last meal on the eve should be 4-6 hours before bedtime. After dinner and until the moment of blood donation (the next day), only pure water (not tea, coffee, juices or other drinks) is allowed.
• During the day before donating blood, you should refrain from drinking alcoholic beverages (including beer). Heavy physical activity is also undesirable.
• Your doctor may tell you to stop taking certain medications 1 or 2 days before your blood test (if possible). If it is impossible to cancel the medicine, then the decoding of the data obtained is done with a correction for this circumstance.
• You should refrain from smoking 1-3 hours before donating blood. Also avoid stress, excitement, fast climbing stairs and any strenuous physical activity.

Norm of C-reactive protein by age and sex

Since C-reactive protein is determined in the blood in response to acute inflammation or an infectious process, its level does not depend on the sex or age of the patient. This means that there are common criteria for assessing CRP for men, women and children.

To assess infectious and inflammatory processes in the body, the level of CRP up to 5 mg/l is considered the norm. As for the assessment of cardiovascular risks, the indicators are different:

• less than 1 mg/l – low risk;
• 1-3 mg/l – medium;
• more than 3 mg / l – increased.

Individuals with elevated CRP but normal LDL have been found to be at greater risk of developing cardiovascular disease than those with normal CRP but elevated LDL. Thus, the CRP indicator in the prognosis of cardiovascular pathologies is much more important than the level of cholesterol.

Causes of elevated C-reactive protein

The main causes of increased CRP are:

• Acute bacterial or viral infections. It has been established that in bacterial infections, the amount of CRP in the blood is higher than in viral ones.
• Exacerbation of chronic infectious and inflammatory diseases.
• Malignant tumors and/or metastases.
• Tissue damage. For example, injuries, acute myocardial infarction, burns or the consequences of surgical operations.
• Sepsis.
• Chronic indolent inflammatory processes (often in the vessels), which increase the risk of cardiovascular disease.
• Overweight and obesity³.
• Autoimmune diseases (rheumatoid arthritis, systemic vasculitis).
• Insulin resistance, prediabetes and diabetes mellitus.
• Violation of the composition of blood lipids (atherogenic dyslipidemia).
• Endocrine diseases and hormonal disorders.
• Smoking and alcohol abuse.

Figure 1 Causes of elevated C-reactive protein levels.

Causes of low C-reactive protein

Low or no CRP may mean no inflammation. Anti-inflammatory drugs (non-steroidal anti-inflammatory drugs, glucocorticoids), statins or beta-blockers are also factors that reduce CRP.

If you are taking these drugs, stop taking them for 1-2 days before testing. This should be done only with the permission of a doctor.

Consequences of deviation of C-reactive protein from the norm

The increase in CRP level itself is a consequence of the development of an infectious-inflammatory process. It is a protective protein that begins to be produced in response to inflammation.

In this case, it is important to make a correct diagnosis. For this, CRP values ​​alone are not enough. This marker only indicates the status of inflammation, and more research is needed for an accurate diagnosis.

Elevated C-reactive protein in coronavirus

The study of CRP levels during the COVID-19 pandemic has gained additional importance. The marker is considered as the main indicator of the activity of the inflammatory process in the lungs. Determination of CRP in patients with COVID-19 allows assessing the following indicators:

• Severity of the course of the disease. If a CRP value of 10 mg/l or more is determined, this indicates a moderate course of the disease. In severe cases, CRP can increase to 100 mg / l or more. At the same time, the level of CRP correlates with the volume of lung tissue damage.
• Monitoring of moderate and severe patients. The level of CRP is determined within a day after the patient’s admission to the hospital. Then, in moderate patients, the analysis is carried out 2 times a week, and in severe patients, every 48 hours.
• Monitoring of the patient’s condition in ARDS. In acute respiratory distress syndrome (ARDS), the level of CRP is determined every 2-3 days. An improvement in the condition is judged by a persistent decrease in the indicator.
• Development of macrophage activation syndrome (MAS). This is a serious condition that threatens the life of the patient. Increasing levels of CRP (in combination with some other markers) may indicate the development of SAM.

The indication for hospital discharge is a CRP level of less than 10 mg/L.

In every second patient with coronavirus, C-reactive protein rises already in the first days of illness. Photo: halfpoint / Depositphotos

How to reduce C-reactive protein

Elimination of factors that increase CRP levels automatically leads to its decrease. These are regular moderate physical activity, giving up bad habits (smoking, excessive drinking) and normalizing body weight.

Timely treatment of acute and chronic diseases also reduces the level of C-reactive protein.

How to increase C-reactive protein

Normally, a healthy person does not have CRP or is found in extremely low concentrations. You don’t need to level up this marker.

Conclusion

C-reactive protein is a highly sensitive marker of the inflammatory process. CRP levels are elevated in infections, inflammation, cancer, diabetes, and a number of other diseases and conditions.

Determine CRP as part of a biochemical analysis. Blood is taken from a vein in the morning, on an empty stomach. When deciphering the analysis, the doctor also takes into account a number of circumstances that can affect the level of CRP in the blood.