C-Reactive Protein (CRP)

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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 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 very well-understood.

High-sensitivity CRP testing is recommended for men over age 50 and women over age 60 who have intermediate risk of having a heart attack in the next 10 years and who have LDL levels less than 3.5 mmol/L.1

A C-reactive protein (CRP) test may also be 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.

How To Prepare

There is no special preparation for a C-reactive protein (CRP) 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 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. ASA, 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 values may vary from lab to lab. Results are usually available within 24 hours.

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

If you are at intermediate risk for heart attack or stroke and your hs-CRP level is above 2 mg/L, your doctor may recommend steps to help you lower your risk. These recommendations may include lifestyle changes and medicines to help lower risk of heart attack or stroke.

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

Less than 1.0 mg/L

Lowest risk

1.0 to 3.0 mg/L

Average risk

More than 3.0 mg/L

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 past health.

Standard CRP levels

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.

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 help find your risk for heart problems, especially when it is considered along other risk factors such as cholesterol, age, blood pressure, and smoking. But the connection between high CRP levels and heart disease risk is not understood very well.

If you are at intermediate risk for heart attack or stroke and your hs-CRP level is above 2 mg/L, your doctor may recommend steps to help you lower your risk. These recommendations may include lifestyle changes such as quitting smoking, eating right, losing weight, and getting more exercise. Your doctor may also prescribe medicine to help you lower your CRP level and reduce your risk for heart attack or stroke.

Other Places To Get Help

Organizations

Canadian Cardiovascular Society
222 Queen Street
Suite 1403
Ottawa, ON  K1P 5V9
Phone: 1-877-569-3407 toll-free
(613) 569-3407
Fax: (613) 569-6574
Web Address: www.ccs.ca
 

The Canadian Cardiovascular Society works to advance the cardiovascular health and care of Canadians through leadership, research, and advocacy.


Heart and Stroke Foundation of Canada
222 Queen Street
Suite 1402
Ottawa, ON  K1P 5V9
Phone: (613) 569-4361
Fax: (613) 569-3278
Web Address: www.heartandstroke.ca
 

The Heart and Stroke Foundation of Canada works to improve the health of Canadians by preventing and reducing disability and death from heart disease and stroke through research, health promotion, and advocacy.


U.S. 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. Genest J, et al. (2009). Canadian Cardiovascular Society/Canadian guidelines for the diagnosis and treatment of dyslipidemia and prevention of cardiovascular disease in the adult—2009 recommendations. Canadian Journal of Cardiology, 25(10): 567–579.

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.
  • 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. Rockville, MD: Agency for Healthcare Research and Quality. Available online: http://www.uspreventiveservicestaskforce.org/uspstf/uspscoronaryhd.htm.

Credits

By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Primary Medical Reviewer Andrew Swan, MD, CCFP, FCFP - Family Medicine
Specialist Medical Reviewer Stephen Fort, MD, MRCP, FRCPC - Interventional Cardiology
Last Revised May 19, 2010

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