A C-reactive protein (CRP) test measures whether infection or inflammation is present in the body. CRP and infection might develop after surgery or when certain medical conditions exist. Blood tests help doctors assess CRP and infection to identify a disorder and evaluate if treatment is working. More sensitive C-reactive protein tests might measure the risk of heart attack from atherosclerosis, which indicates plaque formation in the arteries.
CRP and infection might stem from cancer of the lymph nodes or rheumatoid arthritis. Both conditions cause protein levels in the blood to test higher than normal. Tests might also indicate inflammatory bowel disease, bone infection, pelvic inflammatory disease, or an immune system disorder. CRP and infection symptoms typically rise quickly when a disorder exists and return to normal when treatment begins working.
The connection between CRP and infection might help doctors diagnose patients and serve as a guide for further testing. They commonly use the CRP test to confirm the existence of infection and determine how test results relate to other complaints from patients. Testing CRP and infection also proves useful for patients recovering from organ transplantation and burns to weigh treatment options.
Although the test might provide valuable information, the link between CRP and infection might be affected by a host of outside factors. Certain medications, including hormone replacement therapy drugs and birth control pills, might increase the level of C-reactive protein in the blood. CRP molecules might also be released in women using an intrauterine device to prevent pregnancy or during late stages of pregnancy. Higher CRP levels are also seen in obese patients.
Laboratory tests for CRP and infection might become skewed if blood is drawn immediately after exercise. Physical activity tends to lower the level of the blood protein even when infection is present. Medication to reduce cholesterol levels, and use of aspirin, might also result in CRP levels testing low.
Scientists are not sure why C-reactive protein levels increase in patients with other risks for sudden heart attack. Patients who smoke, suffer from high cholesterol, or high blood pressure typically test high for C-reactive protein in the blood. Some patients with fatty deposits in their arteries might also show elevated protein levels when tested. A highly sensitive CRP test measures heart-attack risks.
Patients who test high for CRP are commonly advised to stop smoking if they use tobacco and begin an exercise program. Some patients are prescribed medication to lower cholesterol levels and blood pressure if those health risks exist. In some cases, daily aspirin might be advised.