A C-reactive protein (CRP) test is used to detect inflammation. It measures levels of CRP, a protein that is released into the blood in response to inflammation. Levels of CRP start to rise soon after the start of inflammation or an infection. Normally, you have low levels of CRP in your blood. 

A CRP test may be ordered if your doctor suspects you have an infection, is checking for an infection after surgery, thinks that you may have an autoimmune disorder such as rheumatoid arthritis or lupus, or is monitoring your treatment of an inflammatory disease to see if it is working.

What is being tested?

C-reactive protein (CRP) is a protein made by the liver and secreted into the blood. It is often the first evidence of inflammation or an infection in the body. Its concentration increases in the blood within a few hours after the start of infection or other inflammatory injury. The level of CRP can increase many hundred-fold in response to inflammation and then drop relatively quickly as soon as the inflammation passes, making it a valuable test to monitor effectiveness of treatment.

How is it used?

CRP is often measured in patients with inflammatory diseases, such as some forms of arthritis and autoimmune diseases or in inflammatory bowel disease. It is used to assess how active the inflammation is and to monitor the treatment. CRP is also used to monitor patients after surgery or other invasive procedures to detect the presence of an infection during the recovery period. CRP tests are not specific enough to diagnose a particular disease. Rather, CRP is a general marker of infection and inflammation that alerts medical professionals that further testing and treatment may be necessary.