C-reactive protein (CRP) by nephelometry (serum/plasma)

C-reactive protein (CRP) is a substance your liver produces when there is inflammation somewhere in your body. Measuring your CRP level gives your doctor a useful window into hidden inflammation, which can be linked to infections, chronic conditions, and heart disease. Understanding your CRP result can help you and your care team make informed decisions about your overall health.

CRP is a marker for inflammation, a natural response your body uses to fight infections, injuries, or other stressors. While CRP itself isn’t harmful, elevated levels often point to underlying issues that need attention. For example, high CRP can be seen in infections, arthritis, heart disease, or even after surgery.

The CRP test is a simple blood test. A healthcare professional draws a small sample of blood, usually from a vein in your arm, and sends it to a laboratory for analysis. The lab measures the amount of C-reactive protein in the sample and reports the result in milligrams per liter (mg/L), with higher levels typically indicating more inflammation in your body.

This test uses a method called nephelometry, which measures how much light scatters when it interacts with CRP particles in your blood. The test is typically done on a sample of your blood drawn from a vein, which is then sent to a lab for analysis.

Doctors order CRP tests for many reasons. The test can help detect infections, monitor chronic inflammatory conditions such as rheumatoid arthritis or lupus, and track how well a treatment is working. A high-sensitivity CRP (hs-CRP) test may also be used to assess your risk of heart disease by detecting low-grade inflammation in your blood vessels.

Doctors often use CRP testing to monitor chronic conditions like rheumatoid arthritis or inflammatory bowel disease. It can also help track how well treatments are working or detect new infections, such as pneumonia or sepsis, especially in people who don’t show obvious symptoms.

In most cases, no special preparation is needed for a CRP blood test. You can usually eat and drink normally beforehand, and you can keep taking your regular medications unless your doctor tells you otherwise. Be sure to mention any recent illness, injury, or medical procedure, since these can temporarily raise your CRP level and affect your results.

There are usually no special preparations needed for this test. You may be asked to fast for 8–12 hours before the blood draw if your doctor recommends it, but this depends on the lab’s protocol. Avoid strenuous exercise or taking anti-inflammatory medications (like ibuprofen) for 24 hours before testing, as these can affect results.