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C-Reactive Protein (CRP)

C-Reactive Protein (CRP)

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. But the connection between high CRP levels and heart attack risk is not understood very well.

How To Prepare

There is no special preparation for a C-reactive protein (CRP) test. You might be asked to not eat or drink for a few hours before the test.

Tell your doctor all of the medicines you are taking because some medicines can affect the results.

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 mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

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 a 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

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Results are usually available within 24 hours.

C-reactive protein (CRP)1
Normal:

Less than 1.0 milligram per deciliter (mg/dL) or less than 10 milligrams per liter (mg/L)

Any condition that results in sudden or severe inflammation may increase your CRP levels.

Some medicines may decrease your CRP levels.

Many conditions can change CRP levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.

High-sensitivity C-reactive protein (hs-CRP) levels

High-sensitivity C-reactive protein (hs-CRP) measures very low amounts of CRP in the blood. This test may help find your risk of heart problems, especially when it is considered along with other risk factors such as cholesterol, age, blood pressure, and smoking. It may be done to find out if you have an increased chance of having a sudden heart problem, such as a heart attack. But the connection between high CRP levels and heart disease risk is not understood very well.

High-sensitivity C-reactive protein (hs-CRP) level1
Normal:

Less than 0.1 mg/dL or less than 1 mg/L

hs-CRP level and heart disease risk2

Less than 1.0 mg/L

Low risk

1.0 to 3.0 mg/L

Average risk

More than 3.0 mg/L

High risk

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

C-reactive protein can be found with this test within a few hours of an inflammation response. So a higher-than-normal CRP level shows a current inflammation. The CRP level drops back to normal when the inflammation goes away.

Other Places To Get Help

Organizations

American Heart Association (AHA)
7272 Greenville Avenue
Dallas, TX  75231
Phone: 1-800-AHA-USA1 (1-800-242-8721)
Web Address: www.heart.org
 

Visit the American Heart Association (AHA) website for information on physical activity, diet, and various heart-related conditions. You can search for information on heart disease and stroke, share information with friends and family, and use tools to help you make heart-healthy goals and plans. Contact the AHA to find your nearest local or state AHA group. The AHA provides brochures and information about support groups and community programs, including Mended Hearts, a nationwide organization whose members visit people with heart problems and provide information and support.



National Heart, Lung, and Blood Institute (NHLBI)
P.O. Box 30105
Bethesda, MD  20824-0105
Phone: (301) 592-8573
Fax: (240) 629-3246
TDD: (240) 629-3255
Email: nhlbiinfo@nhlbi.nih.gov
Web Address: www.nhlbi.nih.gov
 

The U.S. National Heart, Lung, and Blood Institute (NHLBI) information center offers information and publications about preventing and treating:

  • Diseases affecting the heart and circulation, such as heart attacks, high cholesterol, high blood pressure, peripheral artery disease, and heart problems present at birth (congenital heart diseases).
  • Diseases that affect the lungs, such as asthma, chronic obstructive pulmonary disease (COPD), emphysema, sleep apnea, and pneumonia.
  • Diseases that affect the blood, such as anemia, hemochromatosis, hemophilia, thalassemia, and von Willebrand disease.


References

Citations

  1. Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  2. 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.

Other Works Consulted

  • Buckley DI, et al. (2009). C-reactive protein as a risk factor for coronary heart disease: A systematic review and meta-analysis for the U.S. Preventive Services Task Force. Annals of Internal Medicine, 151(7): 483–495.
  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Greenland P, et al. (2010). 2010 ACCF/AHA guideline for assessment of cardiovascular risk in asymptomatic adults: A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Journal of the American College of Cardiology, 56(25): e50–e103.
  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
  • 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.
  • U.S. Preventive Services Task Force (2009). Using nontraditional risk factors in coronary heart disease risk assessment. Available online: http://www.uspreventiveservicestaskforce.org/uspstf/uspscoronaryhd.htm.

Credits

ByHealthwise Staff
Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology
George Philippides, MD - Cardiology
Last RevisedMarch 6, 2012

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.

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