C-reactive protein (CRP) test is a blood test that measures the levels of CRP in the blood. CRP is a protein produced by the liver in response to inflammation or infection in the body. The test is used to detect inflammation, infections, and other medical conditions such as autoimmune diseases, heart disease, and cancer. High levels of CRP in the blood indicate the presence of inflammation, while low levels indicate normal body function. The CRP test is a simple and non-specific test, but it can be helpful in diagnosing and monitoring certain medical conditions.