C-reactive protein (CRP) concentration, measured by nephelometry

Your doctor may order this blood test to look for inflammation somewhere in your body. The C-reactive protein (CRP) test measures the amount of CRP, a protein your liver makes when tissues become inflamed. Results can help detect infections, flare-ups of conditions such as rheumatoid arthritis or inflammatory bowel disease, and other health problems involving inflammation.

Doctors may order a CRP test to monitor conditions like infections (e.g., pneumonia, urinary tract infections), autoimmune diseases (e.g., rheumatoid arthritis), or after surgery to check for complications. It can also help evaluate symptoms like fever, joint pain, or unexplained swelling.

A small sample of your blood is drawn, usually from a vein in your arm, and sent to a laboratory. A machine there measures how much C-reactive protein is in the sample, and the result is reported in milligrams per liter (mg/L). Because CRP rises quickly when inflammation starts, this test often serves as an early warning sign for your care team.

A small blood sample is taken from your arm. The lab uses a method called nephelometry to measure CRP levels. This test is often done on serum or plasma, depending on the lab’s standard procedure.

Most people need no special preparation for a CRP blood test, and you can usually eat and drink as you normally would beforehand. Tell your healthcare provider about any medicines, vitamins, or supplements you take, since some drugs can affect the results. Wearing a shirt with loose sleeves can make it easier for the person drawing your blood.

No special preparation is usually needed, but you may be asked to avoid certain medications (like nonsteroidal anti-inflammatory drugs) that could affect results. If you have a history of bleeding disorders, let your doctor know before the test.

Healthy CRP levels are generally low, and a higher value points to inflammation somewhere in your body. One result cannot show exactly where the inflammation is or what is causing it, so your provider will consider your symptoms, medical history, and possibly other lab work. Your CRP level may also be repeated over time to see whether treatment for an infection or inflammatory condition is working.

CRP levels vary depending on health and activity. Higher levels may indicate inflammation, while lower levels suggest minimal or no inflammation. Your doctor will interpret results in the context of your symptoms and medical history.