A C-reactive protein (CRP) test is done to check for infection after surgery. CRP levels normally rise within 2 to 6 hours of surgery and then go down by the third day after surgery. If CRP levels stay elevated 3 days after surgery, an infection may be present. CRP test is also done to identify and keep track of infections and diseases that cause inflammation, such as cancer of the lymph nodes (lymphoma), diseases of the immune system, such as lupus, painful swelling of the blood vessels in the head and neck (giant cell arteritis), painful swelling of the tissues that line the joints (rheumatoid arthritis), swelling and bleeding of the intestines (inflammatory bowel disease), infection of a bone (osteomyelitis) etc.
A special type of CRP test, the high-sensitivity CRP test (hs-CRP), may be done to find out if you have an increased chance of having a sudden heart problem, such as a heart attack. Inflammation can damage the inner lining of the arteries and make having a heart attack more likely. But the connection between high CRP levels and heart attack risk is not very well-understood.