What Is a C-Reactive Protein (CRP) Test?

When It Is Used and What the Results Indicate

C-reactive protein (CRP) is a protein produced by the liver in response to inflammation. Because high levels of CRP in the blood are reliable indicators of inflammation, a CRP test can be an important first step in diagnosing medical conditions that cause inflammation. This includes infections and autoimmune diseases, such as lupus.

Although the CRP test cannot reveal where the inflammation is occurring or what is causing it, results can point your healthcare provider in the direction of the likely suspects.

This article walks you through the uses of the CRP test, how it is performed, and what to expect before, during, and after the test. It also offers insights into how the results are interpreted so that you can participate in treatment decisions.

what a CRP test can screen for

Verywell / Emily Roberts

Purpose of the Test

The CRP test is a general marker for inflammation. It is used to determine if someone's symptoms are related to an inflammatory or non-inflammatory condition. The results, along with other findings, can help narrow the possible causes.

The CRP level can also tell if the inflammation is acute (severe and sudden, such as with an allergic reaction) or chronic (persistent, such as with diabetes).

Although there are limitations to what the test can reveal, it is a relatively reliable way to measure inflammation. The higher the CRP levels, the greater amount of inflammation in the body.

The CRP test can help identify a wide array of medical conditions, including:

Other Tests

The CRP test is often performed with another blood test called the erythrocyte sedimentation rate (ESR). Both are non-specific markers for inflammation but, together, can offer important clues as to what is going on in the body.

The main difference between the two tests is that changes occur more quickly with CRP. For instance, CRP may drop to normal levels quickly once an infection has cleared, while ESR will remain elevated. In such cases, the ESR can help reveal the "footprint" of an illness even as the symptoms resolve.

There is also a high-sensitivity CRP (hs-CRP) test that measures very low amounts of CRP in order to help predict a person's risk of heart attack and stroke. Together with a cholesterol test, the hs-CRP can help determine if preventive measures, like statin drugs, are needed.

Recap

The CRP test is a non-specific blood test used to measure levels of C-reactive protein, a marker of inflammation. Based on how much CRP levels are raised, a healthcare provider can narrow the possible causes of an illness.

Risks

There are very few risks involved with blood tests. You may experience bruising, swelling, or a hematoma (a pooling of blood under the skin) after the blood draw.

Some people feel dizzy, lightheaded, or even faint.

There is a very small risk of infection from the needle puncture.

Before the Test

Before getting a CRP test, let your healthcare provider know about any medications you take, since some can affect CRP levels.

Timing

A blood draw usually takes less than five minutes. You will be able to leave as soon as the test is complete as long as you're not feeling faint or sick.

Location

The CRP test can be performed in your doctor's office, at a local hospital or clinic, or at a dedicated lab facility.

What to Wear

It is helpful to wear a short-sleeved shirt for the blood draw. Avoid tight sleeves that are difficult to roll or push up.

Food and Drink

A CRP test doesn't require fasting beforehand. However, other blood tests may be performed at the same time that do, such as a fasting cholesterol test. Speak with your healthcare provider or the lab to double-check.

Cost and Health Insurance

A CRP test is relatively inexpensive—around $12 to $16, on average. If you have health insurance, your plan should cover the cost at least in part.

You can find out what your out-of-pocket costs are by calling the number on the back of your insurance card.

What to Bring

Bring a form of ID (such as your driver's license) as well as your insurance card and an approved form of payment, if needed. Check with the lab in advance to find out what kinds of payment they accept.

Recap

The CRP test requires a blood draw performed at a doctor's office or lab. You do not need to fast for this test, although fasting may be needed if other blood tests are being performed. Check with your doctor.

During the Test

The CRP test may be performed by a lab technician, a nurse, or a phlebotomist, a professional who is specially trained to draw blood.

Pre-Test

You may have to fill out some routine paperwork before your test. The receptionist will let you know once you check in.

Throughout the Test

The CRP test takes just a few minutes. Once you're called into the lab, you will sit in a chair. The technician will ask you which arm you want to use.

After a vein, typically one near the crook of your elbow, is chosen. Them the blood draw is performed as follows:

  1. An elastic band is tied around your upper arm to help the vein swell.
  2. The skin is cleaned with an alcohol swab.
  3. A small needle is inserted into the vein. You may feel a slight pinch or poke. If the pain is considerable, let the technician know.
  4. Blood is drawn into a vacuum tube via a thin tube connected to the needle.
  5. After enough blood is taken, the elastic band is taken off and the needle is removed.
  6. Pressure is placed on the puncture site with a cotton ball, after which an adhesive bandage is applied.

Post-Test

Once you feel well enough to do so, you can leave.

If you are feeling lightheaded or faint. let the technician or a member of the staff know.

Recap

The blood draw needed to run a CRP test is performed by a lab technician, nurse, or phlebotomist. If you feel pain, lightheadedness, or dizziness afterward, let the technician know.

After the Test

When you've finished having your blood drawn, you can resume normal activities.

Although there may be swelling, bruising, or pain at the injection site, the side effects tend to be mild and go away within a few days. If they don't or get worse, call your healthcare provider.

Interpreting Results

The results of a CRP or hs-CRP test are typically returned within a day or two, depending on the lab.

CRP Test

The CRP test results may be reported in milligrams per liter (mg/L) or milligrams per deciliter (mg/dL).

Based on the level, a doctor can begin to narrow down the possible causes of an illness. Some of the likely causes can be broken down by the following CRP results:

  • Less than 6 mg/L (0.3 mg/dL): Normal level seen in healthy people
  • 3 to 10 mg/L (0.3 to 1.0 mg/dL): Normal to moderate inflammation (often seen in people who are obese, pregnant, smoke, or have issues like diabetes or the common cold)
  • 10 to 100 mg/L (1.0 to 10 mg/dL): Whole-body inflammation due to autoimmune disease, bronchitis, pancreatitis, heart attack, cancer, or another cause
  • Over 100 mg/L (10 mg/dL): Marked whole-body inflammation due to acute bacterial infections, acute viral infections, systemic vasculitis, or major trauma, among other causes
  • Over 500 mg/L (50 mg/dL): Severe body-wide inflammation most often due to severe bacterial infections

hs-CRP Test

The results of a CRP test are classified as follows to offer a sense of one's risk of a heart attack or stroke:

  • Low risk: Lower than 1.0 mg/L
  • Average risk: 1.0 and 3.0 mg/L
  • High risk: Above 3.0 mg/L

Recap

A CRP test result of 1.0 mg/dL or greater indicates body-wide inflammation. Moderate elevation is anything that falls between 1.0 and 10 mg/dL. Anything more is high or severe elevation.

An hs-CRP result above 3.0 mg/L puts you at high risk for a heart attack or stroke.

Follow-Up

The follow-up of a CRP test can vary based on your diagnosis. Your healthcare provider will consider your CRP results along with your symptoms and medical history, a physical exam, and other lab tests and procedures. The treatment or next steps will depend on that diagnosis.

With respect to the hs-CRP test, a repeat test may be ordered within two weeks since the results can fluctuate. If the results are borderline, the healthcare provider may take a watch-and-wait approach, re-testing after conservative measures like diet and exercise are tried.

If the hs-CRP results are high, they may recommend drugs to help reduce your blood pressure or cholesterol.

Summary

A CRP test is a type of blood test used to measure general inflammation in the body. It does so by detecting a substance called C-reactive protein, which is produced by the liver in response to inflammation.

The CRP test only requires a simple blood draw. The test cannot tell you why or where inflammation is occurring, but it can point to possible causes. There are many, including infection, pancreatitis, an autoimmune disorder, or cancer.

The high-sensitivity CRP is a variation of this test used to predict the risk of heart attack or stroke.

A Word From Verywell

Lab tests can cause stress whenever the findings are abnormal. What is important to remember with the CRP test is that high levels can be caused by many things, some serious and others not. In the end, the test cannot tell you why or where the inflammation is occurring.

Try not to get ahead of yourself and jump to conclusions. Instead, work with your doctor and ask what all of your test results mean. By doing so, you can better understand what your results may (and don't) mean and participate more fully in your treatment decisions.

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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