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C-Reactive Protein

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Also known as: CRP
Formal name: C-Reactive Protein

Were you looking for the high-sensitivity CRP (hs-CRP) test, used to assess your risk of cardiovascular disease?

At a Glance

Why Get Tested?

To identify the presence of inflammation and to monitor response to treatment for an inflammatory disorder

When to Get Tested?

When your healthcare provider suspects that you have an acute condition causing inflammation, such as a serious bacterial or fungal infection or when you are suffering from an inflammatory disorder such as arthritis, an autoimmune disorder, or inflammatory bowel disease

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

C-reactive protein (CRP) is an acute phase reactant, a protein made by the liver and released into the blood within a few hours after tissue injury, the start of an infection, or other cause of inflammation. Markedly increased levels are observed, for example, after trauma or a heart attack, with active or uncontrolled autoimmune disorders, and with serious bacterial infections like sepsis. The level of CRP can jump as much as a thousand-fold in response to inflammatory conditions, and its rise in the blood can precede pain, fever, or other clinical indicators. The test measures the amount of CRP in the blood and can be valuable in detecting inflammation due to acute conditions or in monitoring disease activity in chronic conditions.

The CRP test is not diagnostic, but it provides information to a health practitioner as to whether inflammation is present. This information can be used in conjunction with other factors such as signs and symptoms, physical exam, and other tests to determine if someone has an acute inflammatory condition or is experiencing a flare-up of a chronic inflammatory disease. The health practitioner may then follow up with further testing and treatment.

This standard CRP test is not to be confused with an hs-CRP test. These are two different tests that measure CRP and each test measures a different range of CRP level in the blood for different purposes:

  • The standard CRP test measures markedly high levels of the protein to detect diseases that cause significant inflammation. It measures CRP in the range from 10 to 1000 mg/L.
  • The hs-CRP test accurately detects lower levels of the protein than the standard CRP test and is used to evaluate individuals for risk of cardiovascular disease. It measures CRP in the range from 0.5 to 10 mg/L. (See the article on hs-CRP.)

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Devkota, B. (Updated 2014 January 17). C-Reactive Protein. Medscape Drugs & Diseases [On-line information]. Available online at http://emedicine.medscape.com/article/2086909-overview through http://emedicine.medscape.com. Accessed February 2015.

Andreeva, E. and Melbye, H. (2014). Usefulness of C-reactive Protein Testing in Acute Cough/Respiratory Tract Infection An Open Cluster-Randomized Clinical Trial With C-Reactive Protein Testing in the Intervention Group. Medscape Multispecialty BMC Fam Pract. 2014;15(80) [On-line information]. Available online at http://www.medscape.com/viewarticle/826213 through http://www.medscape.com. Accessed February 2015.

Boggs, W. (2014 November 13). C-reactive Protein as Biomarker Might Reduce Antibiotic Use. Medscape Multispecialty Reuters Health Information [On-line information]. Available online at http://www.medscape.com/viewarticle/834810 through http://www.medscape.com. Accessed February 2015.

Genzen, J. (Updated 2014 May). Acute Phase Proteins - Acute Phase Reactants. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/AcutePhaseReactants.html through http://www.arupconsult.com. Accessed February 2015.

Teitel, A. (Updated 2013 February 11). C-reactive protein. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003356.htm through http://www.nlm.nih.gov. Accessed February 2015.

Delves, P. (Revised 2014 November). Components of the Immune System. The Merck Manual Professional Edition [On-line information]. Available online through http://www.merckmanuals.com. Accessed February 2015.

Pagana, K. D., Pagana, T. J., and Pagana, T. N. (© 2015). Mosby's Diagnostic & Laboratory Test Reference 12th Edition: Mosby, Inc., Saint Louis, MO. Pp 306-307.

Sources Used in Previous Reviews
A Manual of Laboratory & Diagnostic Tests. 6th ed. Fischbach F, ed. Philadelphia: Lippincott Williams & Wilkins; 2000: 619-620.

MedlinePlus Medical Encyclopedia. C-reactive protein. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003356.htm.

Nader Rifai, PhD. Department of Laboratory Medicine, Children's Hospital, Boston, MA.

Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp 190-193.

Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Pp 224, 240.

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC, Pg 203.

Makover, M. (Updated 2011 February 10). C-reactive protein. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003356.htm. Accessed October 2011.

(© 1995–2011). Unit Code 9731: C-Reactive Protein (CRP), Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/9731 through http://www.mayomedicallaboratories.com. Accessed October 2011.

Rollins, G. (2009 February). The JUPITER Trial and CRP, Will the Results Change Clinical Practice? Clinical Laboratory News v 35 (2) [On-line information]. Available online at http://www.aacc.org/publications/cln/2009/February/Pages/CovStory2Feb09.aspx through http://www.aacc.org. Accessed October 2011.

Ridker, P. (2009 February). C-Reactive Protein: Eighty Years from Discovery to Emergence as a Major Risk Marker for Cardiovascular Disease. Clinical Chemistry 55:2 209–215 (2009) [On-line information]. Available online at http://www.clinchem.org/cgi/reprint/55/2/209 through http://www.clinchem.org. Accessed October 2011.

Lowry, F. (2010 March 23). CRP Test Guides Antibiotic Prescribing for Respiratory Tract Infections. From Medscape Medical News [On-line information]. Available online at http://www.medscape.com/viewarticle/719005 through http://www.medscape.com. Accessed October 2011.

Lee, C. and Hammel, J. (Updated 2011 April 15). Temporal Arteritis in Emergency Medicine. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/809492-overview through http://emedicine.medscape.com. Accessed October 2011.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 319-321.