C-reactive protein (CRP) by nephelometry

Doctors order a C-reactive protein (CRP) test to check for signs of inflammation in your body. It can help detect infections, autoimmune conditions, and other health problems, and it is often repeated to see how well a treatment is working over time.

Your doctor may order this test to check for signs of inflammation, assess risk for heart disease, or monitor conditions like arthritis, infections, or other inflammatory diseases. High-sensitivity CRP is particularly useful for detecting mild inflammation that might not be obvious otherwise.

A high CRP level usually means there is inflammation somewhere in your body, which may be caused by an infection, an injury, or a chronic condition such as rheumatoid arthritis or inflammatory bowel disease. A normal or low result generally suggests that no significant inflammation is present, but your doctor will interpret your result alongside your symptoms and other test findings.

A higher-than-normal CRP level may indicate inflammation, infection, or autoimmune conditions. A very low level might suggest no active inflammation, but it doesn’t rule out other health issues. Results alone don’t diagnose a condition—they’re part of a bigger picture.

A health care professional will draw a small sample of blood from a vein in your arm, usually on the inside of your elbow. The sample is sent to a laboratory for analysis, and results are often ready within a day or two. The procedure takes only a few minutes and carries very little risk.

A blood sample is drawn from a vein, usually in your arm. The blood is processed to measure CRP levels using a specialized nephelometry method, which detects the protein’s presence in your serum or plasma.

Several factors can influence CRP levels, including a recent infection, surgery, injury, intense exercise, pregnancy, obesity, and certain medicines such as hormone therapy or statins. Tell your doctor about any recent illness and all medications or supplements you take, because these can change your results.

Factors like recent illness, infection, stress, smoking, or certain medications (e.g., steroids) can temporarily raise CRP levels. Avoiding physical activity or infections for a few days before testing can help get more accurate results.