C-reactive protein (CRP) by nephelometry

Why This Test Is Done

Your doctor may order CRP testing to diagnose or monitor conditions such as infections (like pneumonia or urinary tract infections), inflammatory diseases (like rheumatoid arthritis or lupus), or to assess risk for heart disease. It can also help guide treatment decisions, such as adjusting medications for conditions like autoimmune diseases.

What to Expect Before the Test

No special preparation is needed for this blood test. You may be asked to fast for 8–12 hours before the draw if your lab uses a fasting protocol, but CRP levels don’t change significantly with fasting. Bring any medications or supplements you’re taking to your appointment.

What Happens During the Test

A healthcare provider will draw blood from a vein in your arm using a small needle. You may feel a brief pinch, but the procedure usually takes less than five minutes. The blood is then sent to a lab for analysis using nephelometry, a method that measures how much light a protein scatters.

What the Results Mean

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