C-reactive protein (CRP) is a substance produced by the liver in response to inflammation in the body. It is part of the immune system and helps to identify and respond to infections or injuries. Doctors often measure CRP levels through a blood test to assess inflammation and monitor various health conditions. Elevated levels of CRP can indicate a range of issues, including infections, chronic inflammatory diseases, and even heart disease. However, CRP is a nonspecific marker, meaning it does not pinpoint the exact cause of inflammation, so further testing may be needed for a complete diagnosis.