Patient education: C-reactive protein test (The Basics)

What is a C-reactive protein test? — A C-reactive protein or "CRP" test is a blood test to check for inflammation in the body. When tissue in the body is damaged, the liver releases CRP into the blood. Inflammation damages tissue in the body.

Inflammation can be caused by many different problems. Because of this, a CRP test cannot tell you exactly what health problem you have. It can only show if there is inflammation in the body.

Some conditions that cause inflammation include:

●Infection

●Certain autoimmune diseases – An "autoimmune" disease is when cells in the body's infection-fighting system, called the immune system, start attacking the body's own healthy cells. This causes inflammation. Examples include rheumatoid arthritis and lupus.

●Some types of cancer

Your doctor or nurse might want you to have a CRP test if they think that you might have 1 of these conditions.

There is also a version of this test called "hs-CRP" or "high-sensitivity CRP." This can help figure out your risk for certain cardiovascular problems, such as heart attack or stroke. If you are at high risk of having a heart attack, your doctor or nurse might want you to have an hs-CRP test. You might need to repeat the hs-CRP test multiple times.

How do I prepare for a CRP test? — For this test, you will need to get a "blood draw." Your doctor or nurse will tell you where to go for this. They might tell you to avoid eating or drinking for 8 to 12 hours before the test.

It might help to wear a short-sleeve shirt to your blood draw appointment. This makes it easier for the person drawing your blood to get to your arm.

What happens during a blood draw? — For the blood draw, a needle is used to take a small amount of blood from your arm (figure 1). Collecting the blood only takes a few minutes. The blood is then tested in a lab.

Tell the person who takes your blood:

●If you take "blood thinner" medicines or if you have a bleeding problem – They will make sure that your bleeding is under control before you leave.

●If you have a latex allergy – Some of the supplies used for blood draws might contain latex.

●If you have a preferred arm to use

Most of the time, getting blood taken does not cause problems. You might have a little soreness or bruising where the needle went in.

What do my results mean? — Your doctor or nurse will tell you when to expect your results, and will contact you with the results. Or, if you use an online "patient portal," you might get an alert there when your results are ready.

If you had an hs-CRP test, it will always give a number about 10 times higher than a regular CRP test. This is because of how the measurement is done.

If your CRP or hs-CRP test shows any abnormal results, your doctor or nurse will talk to you about what to do next. They might need to do more tests to figure out what the cause is.

If you do have a health problem, your doctor will work with you to come up with a plan for treatment.

More on this topic

Patient education: Lupus (The Basics)
Patient education: Rheumatoid arthritis (The Basics)
Patient education: Stroke (The Basics)
Patient education: Transient ischemic attack (The Basics)
Patient education: Heart attack (The Basics)
Patient education: Coronary artery disease (The Basics)

Patient education: Systemic lupus erythematosus (Beyond the Basics)
Patient education: Rheumatoid arthritis symptoms and diagnosis (Beyond the Basics)
Patient education: Rheumatoid arthritis treatment (Beyond the Basics)
Patient education: Stroke symptoms and diagnosis (Beyond the Basics)
Patient education: Transient ischemic attack (Beyond the Basics)
Patient education: Heart attack (Beyond the Basics)