- This test can be done on serum(clotted blood 3-5ml).
- It is advisable to perform the test on the fresh sample.
- Serum Can be stored at 4 °C for < 72 hours.
- This can be stored at -20 °C for 6 months.
- Avoid hemolyzed or lipemic samples.
- Keep in mind that:
- Cigarettes smoking may increase the level.
- Estrogen and progesterone may increase the level.
- Niacin and statin may decrease the value.
- There may be an increased level of CRP in hypertension, diabetes mellitus, and metabolic syndrome.
- Avoid lipemic or hemolyzed samples.
Purpose of the test
- This is done in inflammatory diseases like acute rheumatic fever or rheumatoid arthritis and bacterial infection.
- It will help in the diagnosis of coronary artery disease.
- This test can be done to diagnose bacterial endocarditis.
- To diagnose appendicitis.
- To diagnose active collagen vascular diseases.
- C-reactive protein name is derived from its reaction with streptococcal capsular (C) polysaccharides.
- CRP is the fastest responding acute phase protein, as with infection it increases 100 folds time.
- So this is the most sensitive indicator.
- This increases in many diseases so this has no specificity.
- This is nonspecific acute phase protein which has gamma mobility and is very helpful in the monitoring of inflammation.
- C-reactive protein on serum electrophoresis is found in the gamma region.
- CRP is synthesized in the liver and its synthesis is initiated by antigen complexes.
- CRP form complex on the surface of bacteria (E.coli, S.pneumoniae), fungi and another microorganism.
- C R P level increases almost 1000 folds or more in response to severe trauma, bacterial infections, inflammation, surgery, or Neoplastic cells proliferation.
- This does not consistently rise in the viral infection.
- This complexed CRP is a potent opsonin for monocytes, leading to phagocytosis activating the complement system.
- It activates the classical complement pathway.
- CRP also leads to binding of T- lymphocytes, inhibition of clot retraction, suppression of platelets and lymphocytes function, and increase phagocytosis by the neutrophils.
- It increases in the first 12 hours of the infection.
- It will fall within 2-3 days of the inciting event. Therefore it can be used to follow the response to therapy (antibiotics or activity of disease and chronic disease).
- CRP precede the rise in ESR while in the recovery it is the reverse.
- CRP half-life is 5 to 7 hours. So it falls rapidly than the other acute phase protein when mostly have a half-life of 2 to 3 days.
- CRP increases 4 to 6 hours after the surgery and begins to decrease after 3 to 4 days pf postop surgery.
- If the level does not come down then suspect infection or pulmonary infarction.
- CRP helps in the differential diagnosis of bacterial meningitis versus viral meningitis.
- In viral meningitis, CRP is mostly normal which will exclude bacterial meningitis.
- CRP can be used to monitor:
- Rheumatic fever.
- Crohn's disease.
- Rheumatoid arthritis.
- Ankylosing spondylitis.
- Reiter's syndrome.
- Psoriatic arthropathy.
- Still's disease.
- Normally it is negative or < 1 mg/dl.
- Cardiac risk:
- Low < 1.0 mg/dl
- average level 1.0 to 3.0 mg/dl
- High level > 3 mg /dl
- Normal = <1 mg/dL
- For conversion to SI units x 10 = mg/L
CRP Versis ESR:
- It is more sensitive than ESR.
- CRP level increases before there is a rise in antibody titer and ESR.
- In acute inflammatory response, CRP rises earlier than ESR.
- CRP disappear when the inflammatory response is suppressed whereas ESR may take more time.
Coronary artery disease:
- The CRP level increase in the myocardial infarction and its level correlates with the level of myocardial infarction enzymes (Isoenzyme CK-MB).
- If CRP level persists that may indicate ongoing damage to the heart muscles.
- CRP will be normal in Angina.
- CRP baseline level is a good predictor of cardiovascular disease than even low-density lipoprotein (LDL).
Increased values are seen in:
- It is raised in Inflammation, necrosis or tissue injury.
- Acute, noninfectious diseases like arthritis, acute rheumatic fever, and Crohn's disease.
- Collagen vascular diseases like lupus erythematosus and vasculitis.
- Acute myocardial infarction.
- Bacterial infections like postoperative wound infection, urinary tract infection, or tuberculosis and meningitis.
- Pulmonary infarction.
- Malignant diseases.
- Transplant rejection (kidney or bone marrow).
- Active Rheumatic disease (Rheumatoid Arthritis, Rheumatic fever).
- Burns complicated with infection.
- Infection in immunocompromised patients.
- Postoperative complication like a subphrenic abscess or septicemia.
Decreased values are seen in:
- Use of steroids and non-steroidal anti-inflammatory drugs can significantly lower the CRP level.
CRP level is useful in:
- clinical evaluation of SLE, Leukaemia, Blast crisis and ulcerative colitis.
- There is a good correlation with ESR, but CRP appears and disappears earlier than changes in ESR.
- The level of CRP increases dramatically than others Acute phase protein. So CRP is more useful for the acute phase proteins.
- The quantitative test is more useful than a qualitative test.
Jones criteria for the diagnosis of Rheumatic fever:
||Signs and symptoms
||Polyarthritis, carditis, subcutaneous nodule, chorea, Erythema marginatum
||Fever and arthralgia
||Raised CRP, raised ESR, evidence of group A streptococcal infection and prolonged PR interval on ECG
Interpretation: For the diagnosis of rheumatic fever, two major manifestations or one major and two minor manifestations are needed.
Possible References Used
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