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Sample

Precautions

  1. Keep in mind that:
    1. Cigarettes smoking may increase the level.
    2. Estrogen and progesterone may increase the level.
    3. Niacin and statin may decrease the value.
    4. There may be an increased level of CRP in hypertension, diabetes mellitus, and metabolic syndrome.  
  2. Avoid lipemic or hemolyzed samples.

Purpose of the test

  1. This is done in inflammatory diseases like acute rheumatic fever or rheumatoid arthritis and bacterial infection.
  2. It will help in the diagnosis of coronary artery disease.
  3. This test can be done to diagnose bacterial endocarditis.
  4. To diagnose appendicitis.
  5. To diagnose active collagen vascular diseases.

Pathophysiology

  1. C-reactive protein name is derived from its reaction with streptococcal capsular (C) polysaccharides.
    1. CRP is the fastest responding acute phase protein, as with infection it increases 100 folds time.
    2. So this is the most sensitive indicator.
    3. This increases in many diseases so this has no specificity.
  2. This is nonspecific acute phase protein which has gamma mobility and is very helpful in the monitoring of inflammation.
    1. C-reactive protein on serum electrophoresis is found in the gamma region.

  1. CRP is synthesized in the liver and its synthesis is initiated by antigen complexes.
  2. CRP form complex on the surface of bacteria (E.coli, S.pneumoniae), fungi and another microorganism.

  1. C R P level increases almost 1000 folds or more in response to severe trauma, bacterial infections, inflammation, surgery, or Neoplastic cells proliferation.
    1. This does not consistently rise in the viral infection.
  2. This complexed CRP is a potent opsonin for monocytes, leading to phagocytosis activating the complement system.
  3. It activates the classical complement pathway.

                          

  1. CRP also leads to binding of T- lymphocytes, inhibition of clot retraction, suppression of platelets and lymphocytes function, and increase phagocytosis by the neutrophils.
  2. It increases in the first 12 hours of the infection.
    1. 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).
    2. CRP precede the rise in ESR while in the recovery it is the reverse.     
    3. 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.
  3. CRP increases 4 to 6 hours after the surgery and begins to decrease after 3 to 4 days pf postop surgery.   
    1. If the level does not come down then suspect infection or pulmonary infarction.     
  4. CRP helps in the differential diagnosis of bacterial meningitis versus viral meningitis. 
    1. In viral meningitis, CRP is mostly normal which will exclude bacterial meningitis.   
  5. CRP can be used to monitor: 
    1. Rheumatic fever.
    2. Crohn's disease.
    3. Rheumatoid arthritis.
    4. Ankylosing spondylitis.
    5. Reiter's syndrome.
    6. Psoriatic arthropathy. 
    7. Still's disease.

Normal

Source 2

Source 2

 CRP Versis ESR:

  1. It is more sensitive than ESR.
  2. CRP level increases before there is a rise in antibody titer and ESR.
  3. In acute inflammatory response, CRP rises earlier than ESR.
  4. CRP disappear when the inflammatory response is suppressed whereas ESR may take more time.

Coronary artery disease:

  1. The CRP level increase in the myocardial infarction and its level correlates with the level of myocardial infarction enzymes (Isoenzyme CK-MB).
  2. If CRP level persists that may indicate ongoing damage to the heart muscles.
  3. CRP will be normal in Angina.
  4. CRP baseline level is a good predictor of cardiovascular disease than even low-density lipoprotein (LDL).

Increased values are seen in:

  1. It is raised in Inflammation, necrosis or tissue injury.
  2. Acute, noninfectious diseases like arthritis, acute rheumatic fever, and Crohn's disease.
  3. Collagen vascular diseases like lupus erythematosus and vasculitis.
  4. Acute myocardial infarction.
  5. Bacterial infections like postoperative wound infection, urinary tract infection, or tuberculosis and meningitis.
  6. Pulmonary infarction.
  7. Malignant diseases.
  8. Transplant rejection (kidney or bone marrow).
  9. Active Rheumatic disease (Rheumatoid Arthritis, Rheumatic fever).
  10. Burns complicated with infection.
  11. Infection in immunocompromised patients.
  12. Postoperative complication like a subphrenic abscess or septicemia.

Decreased values are seen in:

CRP level is useful in:

  1. clinical evaluation of SLE, Leukaemia, Blast crisis and ulcerative colitis.
  2. There is a good correlation with ESR, but CRP appears and disappears earlier than changes in ESR.
  3. The level of CRP increases dramatically than others Acute phase protein. So CRP is more useful for the acute phase proteins.
  4. The quantitative test is more useful than a qualitative test.

Jones criteria for the diagnosis of Rheumatic fever:

Manifestations Signs and symptoms
Major  Polyarthritis, carditis, subcutaneous nodule, chorea, Erythema marginatum 
Minor Fever and arthralgia
Minor 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.


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