C-Reactive Protein (CRP), High-Sensitivity C-Reactive Protein (hs-CRP), Acute Phase Protein

Acute-phase protein (Acute Phase Reactants)

• Acute-phase protein is raised in inflammatory conditions.
• When there is an increase in a protein called positive acute-phase protein.
  • In the case of a decrease in the acute phase protein, is called negative phase protein.
• The acute phase proteins (positive) are protein whose concentration increases in the plasma and after the disease episode is over then it decreases and may become normal.

C-Reactive Protein (CRP)

Sample

• The venous blood of the patient is needed to prepare the serum.
• A random sample can be taken.
• Analyze the fresh sample.
  • Or can store at 4 °C for <72 hours.
  • At -20 °C for 6 months.

Indication

1. Advised in bacterial infection.
2. It is advised in the rheumatic fever.
3. It is advised in rheumatoid arthritis.
4. May be advised after the surgery.

Precautions

1. This may be raised in cigarette smoking.
2. Avoid hemolysed and lipemic samples.
3. Raised values are seen in hypertension, diabetes mellitus, metabolic syndrome, gingivitis, and bronchitis.
4. Decreased values have seen weight loss, moderate consumption of alcohol, and exercise.
5. Estrogens and progesterone increase value.
6. NIacin, statin, and fibrates decrease value.

Pathophysiology

1. This is found in the Gamma-region band.

2. CRP  was given the name in 1941 that it is protein.
   1. This is a nonspecific acute-phase protein.
   2. CRP is functionally analogous to IgG, except it is not antigen-specific.
   3. hs-CRP detects the lower level of CRP which is important to find the risk of cardiac events.
      1. hs-CRP is useful for the risk of developing acute myocardial infarction with the history of acute coronary syndrome.
3. This protein is synthesized in the liver and released into blood circulation after tissue injury in a few hours.
   1. This synthesis of the CRP is initiated by:
      1. Antigen immune complexes.
      2. Bacterial infection.
      3. Fungal infection.
      4. Trauma or tissue injury.
4. This is the first acute phase protein raised in the inflammatory diseases and its level increases tremendously.
   1. This is raised in acute and chronic inflammation.
5. This promotes the binding of Complement and helps in the phagocytosis.
   

   CRP role in the activation of complement

7. Its formation is initiated by the antigen-antibody immune complex.

8. This can induce the production of cytokines.
9. This can cause inhibition of chemotaxis and modulation of the WBC function.
10. The normal CRP level is <2 to 3 mg/L.
    1. The markedly raised the level of >10 mg/L indicates an active inflammatory condition like collagen diseases and infection.
    2. Its level does not rise consistently in the virus infection.
11. More sensitive and rapidly responding than the ESR.
    1. In the acute inflammatory process, CRP shows an earlier and more rapid increase than the ESR.
    2. In recovery, it becomes normal before the ESR.
    3. It disappears when the disease is treated with cortisone or salicylates.
12. It may be advised after the surgery when its level increases in 4 to 6 hours.
    1. It starts going down after a 3rd postoperative day.
    2. If it persists raised level which indicates a complication of infection or pulmonary infarction.
13. It helps in the differential diagnosis of bacterial or viral meningitis.
    1. In viral meningitis, it will be not raised.
    2. Normal value excludes bacterial meningitis.
14. In myocardial infarction, CRP is raised and it correlates with CK-MB isoenzyme.
    1. Its peak level occurs 1 to 3 days later than CK-MB.
    2. If the level persists to be raised indicates ongoing damage to myocardial tissue.
    3. The baseline level is a good marker for future cardiovascular disease.
       1. CRP is a strong predictor of cardiovascular diseases than the low-density-lipoprotein (LDL), and cholesterol.
       2. In patients with stable coronary disease, CRP is a good marker in case of assessing the likelihood of recurrent myocardial infarction, or restenosis, or death.
    4. Its level is normal in the case of angina.

Normal

• <1.0 mg/dL
• Source 2
  • <1.0 mg/dL or <10.0 mg/L
  • Cardiac disease risk:
    • Low = <1.0 mg/dL
    • Average = 1.0 to 3.0 mg/dL
    • High = >3.0 mg/dL
• Source 4
  • CRP = <0.8 mg/dL  (by nephelometry)
  • CRP repotable value = 0.3 to 20 mg/dL
    • hs-CRP = 0.020 to 0.800 mg/dL (by immunoassay)

Raised level is seen in:

7. 1. Soft tissue Trauma.
   2. Infection.
   3. Tissue necrosis.
8. 1. patients with Rheumatoid arthritis.
   2. In Rheumatic fever.
   3. Patients with systemic lupus erythematosus.
   4. Patient with pneumonia.
   5. patient with malignancies.
   6. In pregnant ladies.
   7. Pulmonary tuberculosis.
   8. Urinary tract infection.
   9. Myocardial infarction.
   10. Vasculitis syndrome.
   11. Bacterial meningitis.

Decreased CRP level is seen in:

1. This may be seen in the moderate use of alcohol.
2. In weight loss.
3. Excessive exercise.
4. Medicine like Niacin, and a statin.

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