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  • Also Known As:
  • CRP
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Test Quick Guide

The C-reactive protein (CRP) test measures the amount of CRP in your blood. CRP is a type of protein that is associated with inflammation in the body. CRP is measured using a small blood sample drawn from a vein in your arm.

Your doctor might order a CRP test if you have symptoms of inflammation. Doctors also use CRP levels to guide treatment of a bacterial infection or to monitor inflammatory processes that occur in some autoimmune diseases.

About the Test

Purpose of the test

Doctors measure CRP because it is a marker of inflammation, which is part of the body’s fight against illness or injury. Your doctor might order a CRP test to:

  • Check for infection if you have symptoms of inflammation such as fever, chills, redness or flushing, nausea, vomiting, rapid breathing, and/or rapid heart rate
  • Guide treatment of sepsis, a life-threatening complication where the body’s response to a bacterial infection triggers inflammation throughout the body
  • Monitor flare-ups of a chronic inflammatory autoimmune disease such as lupus or rheumatoid arthritis
  • Assess the treatment of a chronic inflammatory condition

What does the test measure?

A C-reactive protein test measures the amount of CRP in your blood. CRP levels can reflect the presence and severity of inflammation in your body.

CRP is a protein produced by the liver. When bacteria or other cellular invaders threaten the body, the liver releases CRP into the bloodstream to help organize the body’s defenses. This early response is called an acute phase response. It is also referred to as inflammation or an inflammatory response. The acute phase response also can occur in chronic conditions, including some autoimmune diseases.

As an early responder, CRP is technically known as a positive acute phase reactant. Its level, measured from a blood sample, gives your doctor information about the presence of inflammation and how serious it is. However, CRP levels do not tell the doctor where in your body the inflammation is located or what is causing it.

High-sensitivity CRP (hs-CRP) testing is a different form of testing that identifies very low concentrations of CRP. Although both tests measure CRP, hs-CRP is considered a separate test with distinct uses.

When should I have a C-Reactive Protein test?

CRP testing is done primarily to detect or monitor health conditions that are associated with inflammation. For example, a CRP test may be recommended if you have signs and symptoms of:

  • Bacterial or viral infection
  • Autoimmune disease, including rheumatoid arthritis and lupus
  • Minor inflammation associated with a range of issues such as smoking, diabetes, and physical trauma

There are not strict guidelines for when CRP testing is prescribed, so it is important to consult with your health care provider to determine if a CRP test is appropriate in your situation.

Finding a C-Reactive Protein test

How to get tested

C-reactive protein testing is typically performed only after being prescribed by a doctor or other health professional.

After your doctor orders a CRP test, the blood sample can be drawn at a hospital or clinic laboratory or, if you are hospitalized, at your bedside. In some cases, the sample might be collected at your doctor’s office. The measurement of CRP takes place in a laboratory.

Can I take the test at home?

Options are available for at-home CRP testing. For most of these tests, you collect a blood sample at home and then mail it to a laboratory where it can be analyzed.

The blood sample for at-home CRP tests is taken from your fingertip using a very small needle called a lancet. You then apply a drop of blood to a special test paper that can be processed by the lab. Results are usually provided through a secure website or smartphone app.

At-home CRP tests can be purchased without a prescription, but it is generally best to consult with your doctor before taking an at-home CRP test. Your doctor can discuss the appropriateness of testing and help interpret any test results.

How much does the test cost?

Many factors contribute to the cost of a CRP test, including the materials needed to carry out the test, the fee for the phlebotomist who draws your blood, the laboratory’s fee for analyzing the sample, and the fee from your doctor’s office.

Your insurance coverage will determine your out-of-pocket cost. Insurance generally covers CRP testing, but depending on your policy, you might owe a deductible or a copay. If you are in doubt, check with your insurance provider.

If you are uninsured, then discuss the cost with your doctor or with the hospital or laboratory administrator. Some health care institutions have financial advocacy offices that can assist you with concerns about cost.

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Taking the C-Reactive Protein Test

C-reactive protein is measured from a blood sample that comes from a vein. A small amount of blood will be drawn from your arm. The blood draw usually takes place in a hospital or clinic laboratory, but it can also be done in a doctor’s office or at the bedside in a hospital. The blood draw takes only a few minutes.

Before the test

Your doctor’s office may review your medications before the test. Some medications, including nonsteroidal anti-inflammatory drugs and statins, can impact CRP levels. Magnesium supplements also can affect your CRP level. For this reason, make sure to tell your doctor about any medications or supplements that you take and ask whether you should adjust your medications before the test.

During the test

A phlebotomist will take a blood sample from a vein in your arm. The phlebotomist will place a rubber tourniquet around your upper arm and ask you to pump your fist a few times so that the vein can be located. The technician will cleanse that area of your arm with an alcohol wipe and, when the skin is dry, insert a needle and draw out a vial of blood.

There may be a brief pinching sensation when the needle is inserted. The phlebotomist will then remove the tourniquet, withdraw the needle, briefly apply pressure to the site, and place a bandage over it.

After the test

Providing a blood sample is a routine, low-risk procedure. You might have slight pain or bruising at the injection site, but these symptoms disappear quickly. You will be able to get on with your day and normal activities when you leave the laboratory.

Very rarely, there may be more serious effects such as light-headedness or infection.

These complications are very unlikely, but if you notice any ongoing effects after your test, make sure to contact your doctor.

C-Reactive Protein Test Results

Receiving test results

The results of your CRP test should be available within a business day or two. Depending on your health care provider, you may receive the results via electronic communication or directly from your doctor’s office.

Interpreting test results

Your test result is the level of CRP in your blood. Depending on the laboratory’s standards, the result is expressed in milligrams per deciliter (mg/dL) or milligrams per liter (mg/L). The report might indicate that the level is high, low, or normal.

Although “normal” CRP levels vary from lab to lab, it is generally accepted that a value of 0.8-1.0 mg/dL (or 8-10 mg/L) or lower is normal. Most healthy adults have CRP levels lower than 0.3 mg/dL.

A minor elevation in CRP level—generally 0.3 to 1.0 mg/dL—does not necessarily mean you have an illness that requires treatment. CRP levels may be higher in females, patients on hormone replacement therapy and high body mass index. Mildly elevated CRP can be associated with insomnia and depression. Your doctor will consider these factors when interpreting your CRP test result.

A CRP level higher than 1.0 mg/dL usually suggests that there is inflammation in your body, but it does not identify the cause or the location of that inflammation. Very high levels of CRP can be associated with various types of infections, autoimmune diseases, some cancers, and conditions affecting the lungs or pancreas. If your CRP level is in this range, your doctor may order additional tests to get more information before making a diagnosis.

Because of variations in laboratory methods and reference ranges, it is best to consult with your physician for clarity about your results.

Related Tests

Comparing and contrasting a C-reactive protein test and a high-sensitivity C-reactive protein test

The high-sensitivity C-reactive protein (hs-CRP) test uses a different technique to measure CRP. This allows the hs-CRP test to detect very low elevations of CRP.

Although the substance being measured, CRP, is the same, hs-CRP is a separate test that is used primarily to assess risk of heart disease.

Comparing and contrasting a C-reactive protein test and an erythrocyte sedimentation rate test

The erythrocyte sedimentation rate (ESR) is another way to measure inflammation with a sample of blood. It is a less direct measure than the CRP test. Because the CRP level responds much more quickly to changes in inflammatory activity, it can give doctors more timely information.

The ESR has a role in certain conditions where the information it provides may contribute to the decision-making process. Your physician will decide whether both tests are needed to better understand your condition. Other names for the ESR include SED rate, sedimentation rate, and Westergren sedimentation rate.

Sources

A.D.A.M. Medical Encyclopedia. C-reactive protein. Updated January 31, 2021. Accessed September 15, 2021. https://medlineplus.gov/ency/article/003356.htm

Albert MA, Glynn RJ, Buring J, Ridker PM. C-reactive protein levels among women of various ethnic groups living in the United States (from the Women’s Health Study). Am J Cardiol. 2004;93(10):1238-1242. doi:10.1016/j.amjcard.2004.01.067

American Board of Internal Medicine. ABIM laboratory reference ranges. Updated July 2021. Accessed September 15, 2021. https://www.abim.org/Media/bfijryql/laboratory-reference-ranges.pdf

American Society for Clinical Pathology­­­­­. Choosing wisely. Updated February 3, 2015. Accessed September 15, 2021. https://www.choosingwisely.org/clinician-lists/american-society-clinical-pathology-erythrocyte-sedimentation-rate-for-acute-phase-inflammation/

ARUP Consult. Inflammatory markers. Updated October 2020. Accessed September 20, 2021. https://arupconsult.com/content/inflammatory-markers

Centers for Disease Control and Prevention. What is sepsis? Updated August 17, 2021. Accessed September 20, 2021. https://www.cdc.gov/sepsis/what-is-sepsis.html

Kushner I. Acute phase reactants. In: Furst DE, ed. UpToDate. Updated July 30, 2021. Accessed September 15, 2021. https://www.uptodate.com/contents/acute-phase-reactants

Lapić I, Padoan A, Bozzato D, Plebani M. Erythrocyte sedimentation rate and C-reactive protein in acute inflammation: meta-analysis of diagnostic accuracy studies. Am J Clin Pathol. 2020(1):14-29. doi: https://doi.org/10.1093/ajcp/aqz142

MedLinePlus: National Library of Medicine. C-reactive protein (CRP) test. Updated December 30, 2020. Accessed September 15, 2021. https://medlineplus.gov/lab-tests/c-reactive-protein-crp-test/

Nehring SM, Goyal A, Bansal P, Patel BC. C reactive protein. In: StatPearls. Updated May 10, 2021. Accessed September 15, 2021. https://www.statpearls.com/ArticleLibrary/viewarticle/18744

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