C-Reactive Protein (CRP)

Inflammation is your body's way of protecting your tissues and helping them heal from an injury, infection, or other disease. When it's acute (sudden) and for a short time, inflammation is helpful. For example, when you get a cut on your skin, the area around the cut may turn red and swell. These are signs that inflammation is working to stop infection. Inflammation acts in a similar way when responding to germs or harmful substances (toxins) inside your body.

If inflammation lasts too long, however, it can damage healthy tissues. This is called chronic (long-term) inflammation, and it is most often caused by certain autoimmune disorders. Chronic inflammation can also happen if your tissues are repeatedly injured or irritated, for example from smoking or chemicals in the environment.

In general, healthy people have very low amounts of CRP in their blood. A value of about 1.0 mg/dL (10 mg/L) or lower is considered normal. Higher amounts mean inflammation somewhere in your body.

After an infection or injury, CRP starts to rise within about 6 to 12 hours and peaks within 1 to 2 days. Levels above 100 mg/L often suggest a serious bacterial infection or major tissue injury, while smaller increases are more typical of milder or longer-lasting inflammation.

Your CRP test results tell you how much inflammation you have in your body, but not what's causing it or where it is. CRP can rise with bacterial infections, rheumatic fever, active arthritis, a recent heart attack, certain cancers, or after surgery. To make a diagnosis, your provider will look at your CRP results along with the results of other tests, your symptoms, and medical history.

Watching CRP go down over time can be a useful sign that an infection is responding to antibiotics or that an inflammatory disease is calming down. CRP that stays high can be a warning of an ongoing problem.

A standard CRP test is not designed to pick up the small changes in CRP that are linked to heart disease risk. If your provider wants to estimate that risk, they may order a more sensitive version of the test (often called high-sensitivity CRP).