C-reactive protein (CRP) is a protein made by the liver and released into the blood in response to inflammation. It plays an important role in the immune process.
The CRP test measures the level of a protein in your blood called C-reactive protein (CRP). The level of CRP increases when you have certain autoimmune diseases that cause inflammation, such as arthritis,(external link) inflammatory bowel disease (eg, Crohn's disease(external link) or ulcerative colitis(external link)), or if you have an infection such as pneumonia.(external link)
The serum CRP level in a “healthy” person is usually less than 5 mg per L. This will begin to rise 4–8 hours after tissue is damaged. It peaks within 24–72 hours, and returns to normal 2–3 days after the inflammation or infection has stopped.