C-Reactive protein (CRP) is released from most tissue that is inflamed or under stress. It is a non-specific test but usually indicates significant disease. The normal amount found in the blood is less than 5 mg/L (less than 5 µg/mL).
Higher levels indicate:
- the presence of inflammation anywhere in the body,
- tissue injury,
- rheumatoid arthritis,
- a heart attack (myocardial infarct),
- widespread cancer,
- breast cancer,
- acute gout,
- ankylosing spondylitis,
- rheumatic fever,
- SLE (systemic lupus erythematosus),
- a blood clot in a vein (thromboembolism),
- bacterial meningitis,
- polyarteritis nodosa,
- inflammatory bowel disease (e.g. Crohn disease).
There is now evidence that those with a persistently elevated CRP are at increased risk of heart disease and may benefit from aggressive cholesterol lowering using statin medication.
The ultrasensitive C-Reactive protein is an additional test that is useful in the assessment of angina. Variations in C-reactive protein as low as 0.1 mg/L are measured and rising levels give a poor prognosis for angina and increasing tissue damage in other organs. In patients with angina slowly increasing levels are associated with increasing heart tissue damage even though the total level of CRP may be quite low.