C-reactive protein (CRP) is produced by the liver. The protein may also be synthesized by cells in the vascular wall by the endothelium, smooth muscle cells. Adipose tissues are also known to produce CRP. The gene responsible for the production of the protein is located in the locus 1q23.2 of the chromosome 1.
The level of CRP increases when there is inflammation somewhere in the body. C-reactive protein is one of the proteins called “acute phase reactants”. These substances are produced in response to inflammation.
By the binding to the phosphocholine on the surface of damaged or necrotized cells and some bacteria the protein activates the complement system, promotes phagocytosis and therefore the clearing of dead and injured cells and bacteria.
The acute phase response causes release of cytokines that in turn trigger the synthesis of CRP and fibrinogen by the liver.
The C-reactive protein is known as an early defense system against infections of the innate immunity.
The reference range for C-reactive protein is:
- CRP: 0-10mg/L. Usually CRP is higher in elderly;
- High-sensitivity CRP (hs-CRP): < 3 mg/L;
CRP rises within six to twelve hours of the onset of the underlying condition and reaches its peak at 48 hours. The half-life of the protein is 18 hours. Its level is determined by the rate of production and the severity of the underlying cause. This means that CRP is a marker for inflammation that can be used to screen for inflammation and assessment of the prescribed anti-inflammatory therapy. This fact is probably connected with the chronic vessel lining inflammation associated with atherosclerosis.
|Increased CRP||Decreased CRP|
|Acute or chronic inflammatory conditions|
Tissue necrosis or tissue injury
Ischemia or infarction of tissues (including myocardial infarction)
Pelvic inflammatory disease
Malignant tumors, especially of breast, lung and gastrointestinal tract
Autoimmune disorders (arthritis, lupus, Crohn disease)
Hormone replacement therapy
Oral contraceptives intake
Having intrauterine device
Moderate alcohol consumption
Medications like statins, niacin and fibrates
CRP is used commonly as a marker of inflammation. Liver failure and interferon alpha interfere with CRP production. This results (due to interferon production) in the relatively low levels of CRP found during viral infections compared to bacterial infections. The slightly increased level of CRP (>2.0 mg/L) in the serum indicates the risk of cardiovascular diseases.
|Level of CRP||Condition|
|10–40 mg/L||Late pregnant women, mild inflammation and viral infections|
|40–200 mg/L||Active inflammation, myocardial infarction, bacterial infection|
|>200 mg/L||Severe bacterial infections|
The test is performed in case of:
- When inflammation is suspected (vasculitis, autoimmune disorders, bacterial infection, etc.). CRP is ordered when the symptoms of sepsis, such as fever, chills, and tachypnoe (rapid breathing) and tachycardia (rapid heart rate) are detected;
- CRP may sometimes be ordered along with erythrocyte sedimentation rate (ESR). CRP is a more sensitive indicator of the acute phase response than the ESR. CRP returns to normal sooner than ESR in response to therapy. It is supposed that ESR and CRP levels in serum usually correlate, but in case of viral infection or aseptic lesion SRP rises while ESR remains normal and in case of severe intoxication and chronic arthritis CRP remains normal while ESR grows;
- CRP may also be ordered to monitor chronic inflammatory conditions (rheumatoid arthritis and lupus) and to estimate the treatment effectiveness;
- hs-CRP is performed for patients with some known risk factors of coronary heart disease and the patients with acute coronary syndromes.
The risk of developing cardiovascular disease correlates with the level of CRP:
- low: hs-CRP level under 1.0 mg/L
- average: between 1.0 and 3.0 mg/L
- high: above 3.0 mg/L
Blood samples are taken from the vein by the venepunction.
See also CRP (C-Reactive Protein) test
Measurement methods include:
- Nephelometry (for hs-CRP);
- Rapid immunodiffusion;
- Visual agglutina