C-Reactive Protein (Blood)
Does this test have other names?
What is this test?
The C-reactive protein (CRP) test is used to find inflammation in your body. Inflammation
could be caused by different types of conditions, such as an infection or autoimmune
disorders like rheumatoid arthritis or inflammatory bowel disease. This test measures
the amount of CRP in your blood. CRP is a protein made by the liver and sent into
the bloodstream. Blood levels may be higher when you have inflammation or an infection.
Because CRP levels often go up before you have symptoms of pain or fever and drop
down as you recover, the CRP test is especially useful for tracking infections.
Because CRP is part of the immune system, your levels of it rise whenever you have
inflammation in your body. But the test doesn't show where the inflammation is or
what is causing it.
A high-sensitivity CRP test (hs-CRP) may be used to measure your heart disease risk
even if you seem healthy. It can find much smaller changes in CRP levels than the
regular CRP test.
Why do I need this test?
You may need this test if your healthcare provider thinks you have an infection. For
example, it may be osteomyelitis, which involves bone. Or it may be a potentially
life-threatening condition called sepsis or blood poisoning.
Symptoms of sepsis may include fever and chills, headache, pain, nausea, vomiting,
confusion, rash, and shortness of breath. The level of CRP in your blood goes up within
a few hours of a serious infection. CRP levels can also rise when you have a viral
infection. But they don’t go as high as during a bacterial infection.
Your healthcare provider may also order the test if they think you have an inflammatory
condition or an autoimmune disease, such as rheumatoid arthritis. CRP levels are higher
in people with these conditions. This test may also be used to watch flare-ups and
recovery. Symptoms of rheumatoid arthritis include joint swelling and pain, morning
stiffness, tiredness, weight loss, and low-grade fevers.
If you are being treated for a long-term inflammatory condition or an infection, this
test may be used to see if the treatment is working.
The more specialized CRP test for heart disease risk is not covered in this article.
What other tests might I have along with this test?
Because the CRP test tells you only if you have inflammation and doesn't pinpoint
what is causing it, your healthcare provider will likely order more tests. These may
Erythrocyte sedimentation rate (ESR) test. Like the CRP, this test measures inflammation. It's not as sensitive as the CRP.
But it's easy to do and gives more information. So many healthcare providers will
order it at the same time.
Antinuclear antibody (ANA) test. The ANA test measures autoantibodies that attack your cells. This is important in
diagnosing some autoimmune diseases, such as lupus.
Rheumatoid factor (RF). This test is done to help diagnose and monitor rheumatoid arthritis.
Anticyclic citrullinated peptide (anti-CCP) antibodies. This test is done to help diagnose and monitor rheumatoid arthritis.
What do my test results mean?
Test results may vary depending on your age, gender, health history, and other things.
Your test results may be different depending on the lab used. They may not mean you
have a problem. Ask your healthcare provider what your test results mean for you.
The normal range for this test depends on the lab and the procedure used in the lab.
Generally, a CRP level under 10 milligrams per liter (mg/L) is considered normal.
If the level of CRP in your blood is higher than that, it may mean your body is having
an inflammatory reaction to something. More tests will be needed to figure out what's
causing the inflammation.
How is this test done?
The test is done with a blood sample. A needle is used to draw blood from a vein in
your arm or hand.
Does this test pose any risks?
Having a blood test with a needle carries some risks. These include bleeding, infection,
bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may
feel a slight sting or pain. Afterward, the site may be sore.
What might affect my test results?
A number of things may cause your CRP levels to be slightly higher than normal. These
include obesity, lack of exercise, cigarette smoking, and diabetes.
Certain medicines can cause your CRP levels to be lower than normal. These include
nonsteroidal anti-inflammatory drugs (NSAIDs), aspirin, and steroids.
How do I get ready for this test?
You don’t need to prepare for this test. Be sure your healthcare provider knows about
all medicines, herbs, and supplements you are taking. This includes medicines that
don’t need a prescription and any illegal drugs you may use.