C-Reactive Protein (CRP)

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

Test Preparation Needed?

None

What is being tested?

C-reactive protein (CRP) is a protein made by the liver. CRP levels in the blood increase when there is a condition causing inflammation somewhere in the body. A CRP test measures the amount of CRP in the blood to detect inflammation due to acute conditions or to monitor the severity of disease in chronic conditions.

CRP is a non-specific indicator of inflammation and one of the most sensitive acute phase reactants. That means that it is released into the blood within a few hours after an injury, the start of an infection, or other cause of inflammation. Markedly increased levels can occur, for example, after trauma or a heart attack, with active or untreated autoimmune disorders, and with serious bacterial infections, such as in sepsis. The level of CRP can jump as much as a thousand-fold in response to bacterial infection, and its rise in the blood can precede pain, fever, or other signs and symptoms.

The CRP test is not diagnostic, but it provides information to your healthcare practitioner as to whether inflammation is present, without identifying the source of the inflammation. This information can be used in conjunction with other factors such as signs and symptoms, physical exam, and other tests to determine if you have an acute inflammatory condition or are experiencing a flare-up of a chronic inflammatory disease. Your healthcare 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 high levels of the protein observed in diseases that cause significant inflammation. It measures CRP in the range from 8 to 1000 mg/L (or 0.8 to 100 mg/dL).
The hs-CRP test precisely detects lower levels of the protein than that measured by the standard CRP test and is used to evaluate individuals for risk of cardiovascular disease. It measures CRP in the range from 0.3 to 10 mg/L. (See the article on hs-CRP.)

Common Questions

How is the test used?

The C-reactive protein (CRP) test is used to detect inflammation.

For example, CRP may be used to detect or monitor significant inflammation in acute conditions, such as:

A serious bacterial infection of the lung, urinary tract, digestive tract, skin, or other sites, with or without sepsis
A fungal or viral infection
Pelvic inflammatory disease (PID)

The CRP test is useful in monitoring chronic inflammatory conditions to detect flare-ups and/or to determine if treatment is effective. Some examples include:

Inflammatory bowel disease
Some forms of arthritis, including rheumatoid arthritis
Autoimmune diseases, such as lupus or vasculitis

Examples of other uses:

The CRP test is widely used to detect sepsis in newborn babies.
The CRP test may be used to monitor patients after surgery. Generally, CRP levels increase after surgery and drop down to normal unless post-surgery infection is present.
CRP can be a good predictor of rejection in kidney transplant recipients.

CRP may sometimes be ordered along with an erythrocyte sedimentation rate (ESR), another test that detects inflammation, or procalcitonin, a test that indicates sepsis. While the CRP test is not specific enough to diagnose a particular disease, it does serve as a general marker for infection and inflammation, thus alerting healthcare practitioners that further testing and treatment may be necessary. Depending on the suspected cause, a number of other tests may be performed to identify the source of inflammation.

When is it ordered?

The CRP test may be ordered when it is suspected that you have a serious bacterial infection based on your medical history and signs and symptoms. It may be ordered, for example, when a newborn shows signs of infection or when you have symptoms of sepsis, such as:

Fever, chills
Rapid breathing
Rapid heart rate

It may also be ordered on a regular basis to monitor conditions such as rheumatoid arthritis and lupus and is often repeated at intervals to determine whether treatment is effective. This is particularly useful for inflammation problems since CRP levels drop as inflammation subsides.

It is also ordered and monitored after surgery to ensure that you are free of post-surgery infection.

What does the test result mean?

The level of CRP in the blood is normally low.

Increased CRP level:

A high or increasing amount of CRP in the blood suggests the presence of inflammation but will not identify its location or the cause.
Suspected bacterial infection—a high CRP level can provide confirmation that you have a serious bacterial infection.
Chronic inflammatory disease—high levels of CRP suggest a flare-up if you have a chronic inflammatory disease or that treatment has not been effective.

If the CRP level is initially elevated and drops, it means that the inflammation or infection is subsiding and/or responding to treatment.

What are chronic inflammatory diseases?

"Chronic inflammatory diseases" is a general term used to describe long-lasting or frequently recurring bouts of inflammation associated with a more specific disease. Chronic inflammation can be caused by a number of different conditions such as arthritis, lupus, or inflammatory bowel disease (Crohn disease or ulcerative colitis).

What is the difference between CRP and hs-CRP tests?

Both tests are essentially the same, measuring the same substance in the blood. However, the high sensitivity CRP (hs-CRP) test measures very small amounts of CRP in the blood and is ordered most frequently for seemingly healthy people to assess their potential risk for heart problems. It typically measures CRP in the range from 0.3 to 10 mg/L. The regular CRP test is ordered for those at risk for infections or chronic inflammatory diseases (see above). It measures CRP in the range from 8 to 1000 mg/L (or 0.8 to 100 mg/dL).

What can I do to lower my CRP level?

Make sure to follow the instructions or recommendations of your healthcare provider. CRP levels generally drop down when infection is resolved with treatment.

Can a CRP test be performed in my doctor's office?

It may be performed in a larger clinic, but most CRP tests will be performed in a laboratory.

Is there anything else I should know?

CRP levels can be elevated in the later stages of pregnancy as well as with use of birth control pills or hormone replacement therapy (i.e., estrogen). Higher levels of CRP have also been observed in people who are obese. CRP can also be increased in people who have cancer.

The erythrocyte sedimentation rate (ESR) test will also be increased in the presence of inflammation; however, CRP increases sooner and then decreases more rapidly than the ESR.

Health Professionals – LOINC

LOINC Observation Identifiers Names and Codes (LOINC®) is the international standard for identifying health measurements, observations, and documents. It provides a common language to unambiguously identify things you can measure or observe that enables the exchange and aggregation of clinical results for care delivery, outcomes management, and research. Learn More.

Listed in the table below are the LOINC with links to the LOINC detail pages. Please note when you click on the hyperlinked code, you are leaving Lab Tests Online and accessing Loinc.org.

LOINC	LOINC Display Name
76485-2	CRP [Moles/Vol]
48421-2	CRP (BldC) [Mass/Vol]
1988-5	CRP [Mass/Vol]
14634-0	CRP [Titer]
11039-5	CRP Ql

View Sources

Sources Used in Current Review

2019 review completed by Sami Albeiroti, PhD, DABCC, Scientific Director, Sutter Health Shared Laboratory.

(Mar 01, 2019) Kushner, I. Acute phase reactants. UpToDate. Available online at https://www.uptodate.com/contents/acute-phase-reactants?search=c-reactive%20protein&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1. Accessed March 2019.

Landry, A. Causes and outcomes of markedly elevated C-reactive protein levels. Can Fam Physician. 2017 Jun; 63(6): e316–e323. Available online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5471098/. Accessed March 2019.

Faix, JD. Biomarkers of sepsis. Crit Rev Clin Lab Sci. 2013 Jan; 50(1): 23–36. Available online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3613962/#b32. Accessed March 2019.

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 5th Ed. Burtis CA, Ashwood ER, Bruns DE, eds. St. Louis: Elsevier Saunders.

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. 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. 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. 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. 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. Accessed October 2011.

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. 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. 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. 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. 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. 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.

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