Reactive Protein

An acute-phase reactant glycoprotein, C-reactive protein (CRP) is associated with inflammation. CRP is one of the first proteins to become elevated after an inflammatory process has begun and disappears rapidly when inflammation subsides. In healthy persons, CRP levels are usually less than 0.8 mg/L and are often below the detection limit for standard assays. Serum levels may increase dramatically to exceed 100 mg/L in the presence of bacterial and viral infections, inflammation, severe trauma, surgery, neoplastic proliferation, tissue injury, or necrosis, and transplant rejection. Moderate elevations may be seen with myocardial infarction, autoimmune diseases, rheumatic fever, pregnancy, and postopera-tively, as well as in obese persons and women taking estrogen replacement therapy or with an intrauterine device in place. CRP is not affected by age, race, or food intake and does not have significant circadian variation. Drugs that may reduce or suppress CRP levels by controlling inflammation include statins, fibrates, niacin, nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, salicylates, angiotension-convert-ing enzyme (ACE) inhibitors, and beta-adrenergic blockers. CRP has some advantages over erythrocyte sedimentation rate (ESR). The CRP rises before the ESR, returns to baseline sooner, and is less influenced by altered physiologic states.

The levels of CRP used to assess atherosclerotic risk are much lower than those associated with inflammation (Myers et al., 2004). More sensitive immunoassays were developed to measure levels lower than those detected in conventional assays. These highly sensitive CRP tests (hsCRP; Cardiac-CRP) can accurately measure to a lower limit of 0.3 mg/L. Many studies have found that hsCRP levels predict the long-term risk of myocardial infarction, ischemic stroke, peripheral vascular disease, and all-cause mortality in healthy subjects. The hsCRP also predicts outcomes in patients with stable coronary artery disease, acute coronary syndromes, and after percutaneous coronary intervention. In 2004 the American College of Cardiology and American Heart Association (AHA) recommended hsCRP testing to further evaluate patients judged to be at intermediate risk for the development of coronary heart disease (those with 10-year CHD risk of 10% to 20%). CRP levels are divided into tertiles: low risk (<1.0 mg/L), average risk (1.0-3.0 mg/L), and high risk (>3.0 mg/L). A CRP in the highest tertile is associated with a twofold risk of major coronary events compared with a CRP in the lowest tertile. Unexplained levels of hsCRP levels higher than 10 mg/L should be repeated and evaluated for noncardiovascular causes, such as infection or inflammation (Smith et al., 2004).

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