C-reactive protein in blood (CRP)

c-reactive proteinC-reactive protein in blood (CRP) is a pentameric protein found in the blood plasma that is known to indicate inflammation.


Description


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.

Levels


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;


Causes

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 CRPDecreased CRP
Acute or chronic inflammatory conditions

Tissue necrosis or tissue injury

Atherosclerosis

Ischemia or infarction of tissues (including myocardial infarction)

Infection, inflammation

Pelvic inflammatory disease

Fungal infection

Metabolic syndrome

Malignant tumors, especially of breast, lung and gastrointestinal tract

Acute pancreatitis

Autoimmune disorders (arthritis, lupus, Crohn disease)

Post-surgery period

Burn

Leukemia

Tobacco smoking

Hormone replacement therapy

Oral contraceptives intake

Obesity

Pregnancy

Having intrauterine device

Exercise

Weight loss

Moderate alcohol consumption

Medications like statins, niacin and fibrates

 


Clinical use

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 CRPCondition
0-10mg/LNormal
10–40 mg/LLate pregnant women, mild inflammation and viral infections
40–200 mg/LActive inflammation, myocardial infarction, bacterial infection
>200 mg/LSevere 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

 

The test

Blood samples are taken from the vein by the venepunction.

See also CRP (C-Reactive Protein) test

Measurement methods include:

  • ELISA;
  • Immunoturbidimetry;
  • Nephelometry (for hs-CRP);
  • Rapid immunodiffusion;
  • Visual agglutina