Test Overview
A
C-reactive protein (CRP) test is a blood test that measures the amount of a
protein called C-reactive protein in your blood.
C-reactive protein measures general levels of
inflammation in your body.
High levels
of CRP are caused by infections and many long-term diseases. But a CRP test
cannot show where the inflammation is located or what is causing it. Other
tests are needed to find the cause and location of the inflammation.
Why It Is Done
A C-reactive protein (CRP) test is done
to:
- Check for infection after surgery. CRP levels
normally rise within 2 to 6 hours of surgery and then go down by the third day
after surgery. If CRP levels stay elevated 3 days after surgery, an infection
may be present.
- Identify and keep track of infections and diseases
that cause inflammation, such as:
- Check to see how well treatment is working, such
as treatment for cancer or for an infection. CRP levels go up quickly and then
become normal quickly if you are responding to treatment measures.
A special type of CRP test, the high-sensitivity CRP test
(hs-CRP), may be done to find out if you have an increased chance of having a
sudden heart problem, such as a
heart attack. Inflammation can damage the inner lining
of the arteries and make having a heart attack more likely. However, the
connection between high CRP levels and heart attack risk is not very
well-understood.
How To Prepare
There is no special preparation for a
C-reactive protein (CRP) test.
Talk to your doctor about any
concerns you have regarding the need for the test, its risks, how it will be
done, or what the results will indicate. To help you understand the importance
of this test, fill out the
medical test information form 
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.
How It Is Done
The health professional taking a sample
of your blood will:
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
alcohol.
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
blood.
- Remove the band from your arm when enough blood is
collected.
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure on the site and then put on a
bandage.
How It Feels
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
pinch.
Risks
There is very little chance of a problem from
having blood sample taken from a vein.
- You may get a small bruise at the site. You can
lower the chance of bruising by keeping pressure on the site for several
minutes.
- In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.
- Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (such as
Coumadin), and other blood-thinning medicines can make bleeding more likely. If
you have bleeding or clotting problems, or if you take blood-thinning medicine,
tell your doctor before your blood sample is taken.
Results
A C-reactive protein (CRP) test is a
blood test that measures the amount of a
protein called C-reactive protein in your
blood.
Normal
Normal values may vary from lab to lab.
Results are usually available within 24 hours.
C-reactive protein (CRP) | Normal: | 0–1.0
mg/dL or less than 10
mg/L (SI units) |
|---|
Any condition that results in sudden or severe
inflammation may increase your CRP levels.
Some medicines may
decrease your CRP levels.
High-sensitivity C-reactive protein (hs-CRP) levels
The hs-CRP test measures your risk for heart problems. It may be done to
find out if you have an increased chance of having a sudden heart problem, such
as a
heart attack. However, the connection between high CRP
levels and heart attack risk is not very well-understood.
High-sensitivity C-reactive protein (hs-CRP) levels Less than 1.0 mg/dL | Lowest risk |
|---|
1.0 to 3.0 mg/dL | Average risk |
|---|
More than 3.0 mg/dL | Highest risk |
|---|
Many conditions can change CRP
levels. Your doctor will talk with you about any abnormal results that may be
related to your symptoms and medical history.
What Affects the Test
You may not be able to have the
test or the results may not be helpful if:
What To Think About
- High-sensitivity C-reactive protein (hs-CRP) measures very low
amounts of CRP in the blood. This test may be helpful in predicting your risk
for heart problems, especially when it is combined with
total cholesterol and HDL cholesterol tests.
- High CRP levels before a major surgery may indicate that you are
at risk for developing an infection after surgery.
- CRP testing can
be used to see how well you respond to cancer treatment or treatment for an
infection. Your CRP levels will rise quickly and then quickly return to normal
if the treatment is working.
- High CRP levels may increase your
chances of having other diseases, such as
age-related macular degeneration and
colon cancer.
References
Other Works Consulted
Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed.
Philadelphia: Saunders.
Erlinger TP, et al. (2004). C-reactive protein and the
risk of incident colorectal cancer. JAMA, 291(5):
585–590.
Fischbach FT, Dunning MB III, eds. (2004).
Manual of Laboratory and Diagnostic Tests, 7th ed.
Philadelphia: Lippincott Williams and Wilkins.
Handbook of Diagnostic Tests
(2003). 3rd ed. Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis:
Mosby.
Pearson TA, et al. (2003). Markers of inflammation and
cardiovascular disease: American Heart Association and the Centers for Disease
Control and Prevention scientific statement. Circulation, 107(3): 499–511.
Seddon JM, et al. (2004). Association between
C-reactive protein and age-related macular degeneration. JAMA, 291(6): 704–710.
Credits
| Author | Robin Parks, MS |
| Editor | Kathleen M. Ariss, MS |
| Associate Editor | Tracy Landauer |
| Associate Editor | Pat Truman, MATC |
| Primary Medical Reviewer | E. Gregory Thompson, MD - Internal Medicine |
| Specialist Medical Reviewer | George Philippides, MD - Cardiology |
| Last Updated | March 26, 2008 |
