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 helps your doctor find out whether inflammation is present, how active it may be, and how well a treatment is working, which makes this simple blood test a valuable part of many medical evaluations.

CRP is a marker that rises when your body is fighting inflammation or infection. It’s often used alongside other tests to monitor conditions like rheumatoid arthritis, heart disease, or infections such as pneumonia or sepsis.

A CRP test is a straightforward 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. There, the amount of CRP is measured and reported in milligrams per liter (mg/L), with higher values generally pointing to more inflammation in your body.

Your blood sample is analyzed using nephelometry, a method that measures how much light a protein scatters. Higher CRP levels scatter more light, indicating increased inflammation.

In most cases, very little preparation is needed before a CRP test. You can usually eat and drink normally unless your doctor asks you to combine it with other tests that require fasting. Let your care team know about any medications, supplements, or recent illnesses you have had, since these factors can sometimes influence your results.

No special preparation is needed, but inform your healthcare provider about any medications, recent illnesses, or conditions that might affect results (e.g., infections, recent surgery).

Doctors order CRP testing for many reasons, including checking for infections, monitoring chronic inflammatory conditions such as rheumatoid arthritis or inflammatory bowel disease, and tracking how well treatments like anti-inflammatory medications are working. It may also be used alongside other tests to help evaluate the risk of heart and blood vessel disease.

Doctors may order CRP tests to diagnose or monitor conditions like autoimmune diseases (e.g., lupus), infections, or to evaluate risk for heart disease or stroke. It can also help guide treatment decisions.