C-reactive protein (CRP) concentration in serum/plasma

C-reactive protein (CRP) is measured to look for inflammation somewhere in your body. Doctors often order this test when they suspect an infection or an inflammatory condition such as rheumatoid arthritis, lupus, or inflammatory bowel disease, and it is also used to monitor whether treatment is working over time.

Doctors may order CRP tests to diagnose or monitor conditions like infections (e.g., pneumonia, urinary tract infections), autoimmune diseases (e.g., rheumatoid arthritis), heart disease, or other inflammatory processes. It can also help assess how well treatment is working.

Most people need no special preparation before a CRP blood test, and fasting is usually not required, so you can eat and drink as you normally would. Let your doctor know about any medications, supplements, recent illnesses, or injuries, since these can temporarily raise CRP levels and affect your results.

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if it involves drawing blood from a vein. If testing urine or another specimen, follow any specific instructions your doctor provides.

The test is done with a simple blood draw, usually from a vein in your arm. A healthcare professional will clean the site, tie a band around your upper arm, and collect a small sample into a tube. It takes only a few minutes, and you may feel a quick pinch when the needle goes in. Afterward, a small bandage is applied and you can return to your normal activities.

A healthcare professional will collect a blood sample from a vein in your arm using a needle. The blood is then sent to a lab for analysis. If testing urine or saliva, you’ll provide a sample directly.

CRP levels are typically considered normal when they are below 10 mg/L, although exact reference ranges vary between laboratories. Elevated results point to inflammation, which may come from an infection, an autoimmune condition, or tissue injury, and very high readings are often seen with acute bacterial infections. CRP alone cannot pinpoint the cause, so your doctor will interpret it together with your symptoms and other test results, and may repeat it to track how inflammation responds to treatment.

Results are typically reported in milligrams per liter (mg/L). Higher than normal levels may indicate inflammation, infections, or other health issues. Your doctor will interpret the results in the context of your medical history and symptoms.