C-reactive Protein (CRP) is an acute-phase reactant protein used to indicate an inflammatory illness. It is believed to be of value in predicting coronary events. 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 is functionally analogous to immunoglobulin G, except that it is not antigen specific. CRP interacts with the complement system.
The C-reactive Protein test is a 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 antiinflammatory agents, salicylates, or steroids.
This test is 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 Iinase, 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.
Recent development of a high sensitivity assay for CRP (hs-CRP) has enabled accurate assays at even low levels. 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. 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, High-sensitivity C-reactive Protein measurement may be useful as an independent marker for assessing likelihood of recurrent events, including death, myocardial infarction (MI), or restenosis after percutaneous coronary intervention (PCI).
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 oxidized 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 patients 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 infections. 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.
Normal C-reactive Protein Levels
C-reactive Protein is normally found in very low levels in blood. C-reactive Protein Levels are normally less than 1 mg/dL (or less than 10 mg/L using SI units).
C-reactive Protein Indications of Cardiac Risk
Normal C-reactive Protein Levels are an indication of no or Low Cardiac Risk. When C-reactive Protein Levels exceed the normal range, this would be an indication of a Cardiac Risk. A C-reactive Protein Levels higher than 3 mg/dL is an indication of High Cardiac Risk. C-reactive Protein Levels range between 1 and 3 mg/dL would indicate an average Caridac Risk.
Causes of C-reactive Protein False Indications
- Elevated C-reactive Protein results are normally to be seen in patients with Hypertension, Elevated Body Mmass Index, Metabolic Syndrome (Diabetes Mellitus), Chronic Infection (Gingivitis, Bronchitis), Chronic Inflammation (Rheumatoid Arthritis), and low levels of High-density Lipoprotein (High Triglycerides Levels).
- Cigarette smoking can cause increased C-reactive Protein levels.
- Decreased C-reactive Protein levels can result from moderate Alcohol Consumption, Weight Loss, and increased activity or endurance exercise.
- Medications that may increase C-reactive Protein test results include Estrogens and Progesterones.
- Medications that may decrease C-reactive Protein Test results include Fibrates, Miacin, and Statins.
Causes of High C-reactive Protein Levels
The following diseases are all associated with an inflammatory reaction that instigates the synthesis of CRP:
- Acute, noninfectious Inflammatory Reaction (e.g., Arthritis, Acute Rheumatic fever, Reiter Syndrome, Crohn Disease).
- Collagen-vascular Diseases (e.g., vasculitis Syndrome, Lupus Erythematosus).
- Tissue Infarction or Damage (e.g., Acute Myocardial Infarction, 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 Infection (e.g., Tuberculosis, Meningitis).
Increased risk for Cardiovascular Ischemic events: Inflammation of the intimal lining of a blood vessel, and particularly the coronary vessels, is associated with an increased risk for intimal injury thereby leading to distal vessel plaque occlusions.