C-reactive protein (CRP): Indications, Normal Range, Risk Factors

C-reactive protein (CRP)

What is a c-reactive protein (CRP)?

C-reactive protein (CRP) is a nonspecific, acute-phase reactant protein used to diagnose bacterial infectious disease and inflammatory disorders. Such as acute rheumatic fever and rheumatoid arthritis. It is also elevated when there is tissue necrosis. CRP levels do not consistently rise with viral infections. CRP is a protein produced primarily by the liver during an acute inflammatory process and other diseases. A positive test result indicates the presence, but not the cause, of the disease. The synthesis of CRP is initiated by antigen-immune complexes, bacteria, fungi, and trauma. CRP functionally analogous to immunoglobulin G, except it is not antigen-specific. CRP interacts with the complement system.

        The CRP test is more sensitive and rapidly responding indicator than the erythrocyte sedimentation rate (ESR). In an acute inflammatory change, CRP shows an earlier and more intense increase than ESR; with recovery, the disappearance of CRP precedes the return of ESR to normal. The CRP also disappears when the inflammatory process is suppressed by anti-inflammatory agents, salicylates, or steroids.

        This test also useful in evaluating patients with an acute myocardial infarction (AMI). The level of CRP correlates with peak levels of the MB isoenzyme of creatine kinase, but CRP peaks occur 18 to 72 hours later. Failure of CRP to normalize may indicate ongoing damage to the heart tissue. Levels are not elevated in patients with angina.

        Atheromatous plaques in diseased arteries typically contain inflammatory cells. Multiple prospective studies have also demonstrated that baseline CRP is a good marker of future cardiovascular events. The CRP level may be a stronger predictor of cardiovascular events than the low-density lipoprotein (LDL) cholesterol level. When used together with the lipid profile, it adds prognostic information to that conveyed by the Framingham risk score.

        Recent development of a high sensitivity assay for CRP (hs-CRP) has enabled accurate at even low levels. Because of the individual variability in hs-CRP, two separate measurements are required to classify a person's risk level. In patients with stable coronary disease or acute coronary syndromes, hs-CRP measurement may be useful as an independent marker for assessing the likelihood of recurrent events, including death, myocardial infarction (MI), or restenosis after percutaneous coronary intervention (PCI). hs-CRP is most commonly used when other causes of systemic inflammation have been eliminated.

        Another indicator of inflammation besides CRP that is instigating considerable attention as a cardiac risk factor is lipoprotein-associated phospholipase A2 (Lp-PLA2). Lp-PLA2 promotes vascular inflammation through the hydrolysis of oxidised LDL within the intima, contributing directly to the atherogenic process. When combined with CRP, testing for Lp-PLA2 markedly increases the predictive value in determining risk for a cardiac event, especially in patient whose cholesterol is normal. The PLAC test is an enzyme linked immunosorbent assay (ELISA) using two highly specific monoclonal antibodies to measure the level of Lp-PLA2 in the blood.

        The CRP test also may be used postoperatively to detect wound infection. CRP levels increase within 4 to 6 hours after surgery and generally begin to decrease after the third postoperative day. Failure of the levels to fall is an indicator of complications, such as infection or pulmonary infarction.

C-reactive protein (CRP) Normal Findings

• Levels between 3 mg/L and 10 mg/L are mildly elevated and usually result from chronic conditions such as diabetes, hypertension, or lifestyle factors including tobacco smoking and being sedentary
• Levels between 10 mg/L and 100 mg/L are moderately elevated and are usually due to more significant inflammation from an infectious or non-infectious cause
• Levels above 100 mg/L are severely elevated and almost always a sign of severe bacterial infection

The hs-CRP test results indicate a person’s risk of developing cardiovascular disease accordingly:

• Low risk is less than 1 mg/L.
• Moderate risk is between 1 mg/L and 3 mg/L.
• High risk is greater than 3 mg/L.

Indications 

• C-reactive protein (CRP) is an acute-phase protein used to indicate an inflammatory illness. it is believed to be of value in predicting coronary events.

Interfering Factors

• Elevated test results can occur in patients with hypertension, elevated body mass index, metabolic syndrome/diabetes mellitus, chronic infection (gingivitis, bronchitis), chronic inflammation (rheumatoid arthritis), and low high-density lipoprotein (HDL)/high triglycerides.
• Cigarette smoking can cause increase the levels.
• Decreased test levels can result from moderate alcohol consumption, weight loss, and increased activity or endurance exercise.
• Medication that may increase test results include estrogens and progesterones.
• Medication that may decrease test results include fibrates, niacin, and statins.

Procedure and Patient Care

• Maintain routine blood testing procedure.
• Fasting: verify with Lab.
• Blood tube commonly used: Red.

Test Results and Clinical Significance

C-reactive protein (CRP) Increased Levels

• Acute noninfectious inflammatory reaction (eg. arthritis, acute rheumatic fever, Reiter syndrome, Crohn disease)
• Collagen-vascular disease (eg, vasculitis syndrome, lupus erythematosus).
• Tissue infarction or damage (eg, acute myocardial infarction (AMI), Pulmonary infarction, Kidney or bone marrow transplant rejection, soft-tissue trauma).
• Bacterial infections such as postoperative wound infection, urinary tract infection, or tuberculosis.
• Malignant disease.
• Bacterial infections

References: Mosby's Manual of diagnostic and Laboratory