C-Reactive Protein (CRP) Test

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. Your liver makes CRP in response to inflammation.

Inflammation is your body's way of protecting your tissues and helping them heal from an injury, infection, or other disease. When it's acute (sudden) and for a short time, inflammation is helpful. For example, when you get a cut on your skin, the area around the cut may turn red and swell. These are signs that inflammation is working to stop infection. Inflammation acts in a similar way when responding to germs or harmful substances (toxins) inside your body.

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

Other names: c-reactive protein, serum

What is it used for?

By measuring the levels of c-reactive protein in your blood, a CRP test can tell your health care provider how much inflammation you have in your body. High CRP levels may mean you have an acute or chronic health condition, such as:

• 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.

Smoking and exposure to environmental toxins such as polluted air and hazardous waste can also cause high CRP levels.

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 wants to:

• Check for a chronic condition that causes inflammation.
• Monitor for infection after surgery.
• Monitor your condition and treatment if you have an infection or a chronic condition.
• 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.

CRP levels rise and fall depending on how much inflammation is in your body. So, if your CRP levels fall, it's a sign that your treatment for inflammation is working or that 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 magnesium and non-steroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen and aspirin. 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?

In general, healthy people have very low amounts of CRP in their blood. A value of 0.8-1.0 milligrams per deciliter (mg/dL) or lower is thought to be a healthy amount. Any increases above normal may mean you have inflammation in your body. However, increases can also be linked to:

• Insomnia.
• Depression.
• Hormone replacement therapy.
• Obesity.
• Sex. Females often have slightly higher CRP levels than males.

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

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.