What is a c-reactive (CRP) protein test?

A c-reactive protein test measures the level of c-reactive protein (CRP) in a sample of your blood. CRP is a protein that your liver makes. Normally, you have low levels of c-reactive protein in your blood. Your liver releases more CRP into your bloodstream if you have inflammation in your body. High levels of CRP may mean you have a serious health condition that causes inflammation.

Inflammation is your body's way of protecting your tissues and helping them heal from an injury, infection, or other disease. Inflammation can be acute (sudden) and temporary. This type of inflammation is usually helpful. For example, if you cut your skin, it may turn red, swell, and hurt for a few days. Those are signs of inflammation. Inflammation can also happen inside your body.

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

A CRP test can show whether you have inflammation in your body and how much. But the test can't show what's causing the inflammation or which part of your body is inflamed.

Other names: c-reactive protein, serum

What is it used for?

A CRP test may be used to help find or monitor inflammation in acute or chronic conditions, including:

• Infections from bacteria or viruses
• Inflammatory bowel disease, disorders of the intestines that include Crohn's disease and ulcerative colitis
• Autoimmune disorders, such as lupus, rheumatoid arthritis, and vasculitis
• Lung diseases, such as asthma

Your health care provider may use a CRP test to see if treatments for chronic inflammation are working or to make treatment decisions if you have sepsis. Sepsis is your body's extreme response to an infection that spreads to your blood. It's a life-threatening medical emergency.

Why do I need a CRP test?

You may need this test if you have symptoms of a bacterial infection, such as:

• Fever or chills
• Rapid heart rate
• Rapid breathing
• Nausea and vomiting

You may also need a CRP test if your provider thinks you may have a chronic condition that causes inflammation. The symptoms will depend on the condition.

If you've already been diagnosed with an infection or a chronic disease that causes inflammation, you may need this test to monitor your condition and treatment. CRP levels rise and fall depending on how much inflammation is in your body. If your CRP levels fall, it's a sign that your treatment for inflammation is working or you're healing on your own.

What happens during a CRP test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This process usually takes less than five minutes.

Will I need to do anything to prepare for the test?

Some medicines may affect your results. So, tell your provider about any supplements or medicines that you take, including ibuprofen, aspirin, and other non-steroidal anti-inflammatory drugs (NSAIDS). Don't stop taking any prescription medicines without talking with your provider first.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Your CRP test results tell you how much inflammation you have in your body. But your test results can't tell you what's causing the inflammation. To make a diagnosis, your provider will look at your CRP results along with the results of other tests, your symptoms, and medical history.

In general, healthy people have very low amounts of CRP in their blood. Any increases above normal mean you have inflammation in your body. But labs measure CRP levels in different ways, and they define "normal" CRP ranges differently, so it's best to ask your provider what your results mean.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a CRP test?

A CRP test is sometimes confused with a high-sensitivity-(hs) CRP test. They both measure CRP, but they are used for different conditions. An hs-CRP test measures very tiny increases in your CRP levels. It is used to estimate your risk of heart disease.