Understanding C-Reactive Protein and Test Results

C-reactive protein is a lab test. It involves having blood drawn from an arm vein. Test results can tell your doctor about inflammation in your body. This can help diagnose and monitor conditions that cause inflammation. There is no special preparation for this blood test. Bruising is possible with any blood draw, including for C-reactive protein.

This article explains the C-reactive protein (CRP) test, including its uses, side effects, procedure, and high and low levels.

C-reactive protein is a marker of inflammation. The liver makes it in response to injury or infection somewhere in your body. The liver sends CRP into the blood, where it helps Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source  the body recognize and clear out pathogens or damaged cells.

Levels of CRP rise very quickly once the liver starts making it. The levels will stay high as long as inflammation is present. They fall quickly when inflammation subsides. The level changes make CRP a good direct measure of inflammation.

Doctors can assess the level of CRP in the blood by ordering a C-reactive protein blood test.

Your doctor may order a CRP test if they suspect you have a condition causing inflammation. There are several Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source  acute and chronic conditions that can result in increased CRP levels, including:

• arthritis, including rheumatoid arthritis
• atherosclerosis, which can lead to heart attack
• autoimmune disorders
• chronic or severe acute infections
• gum disease
• inflammatory bowel disease
• sepsis
• sleep disorders
• trauma

If you have a chronic condition involving inflammation, your doctor may use CRP testing to monitor it.

CRP test results present with a reference range or normal range. Comparing your result with this range will tell you whether the level is normal, high, or low. These ranges can vary Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source  from one lab to another, so it is important to check the lab reference range when evaluating results.

A standard CRP test measures CRP in milligrams per liter (mg/L). In general, most healthy adults will have a level of 0.3 mg/L Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source  or lower. The range of 0.3–1.0 mg/L represents a slight elevation. There are several factors that can cause slight CRP elevation, including:

• common cold
• diabetes
• gum disease
• lack of exercise
• obesity
• pregnancy
• smoking

Results for the standard CRP test fall into four categories:

• Slight elevation: 0.3–1.0 mg/L
• Moderate elevation: 1.0–10.0 mg/L
• High elevation: 10 mg/L or higher
• Severe: 50 mg/L

There is also a high sensitivity (hs) CRP test doctors use for assessing heart disease risk. It measures CRP in mg/L. However, its normal and high levels differ from a standard CRP test.

Results for a hs-CRP test generally fall into three categories:

• Low risk: less than 1 mg/L
• Moderate risk: 1–3 mg/L
• High risk: greater than 3 mg/L

If you already know you are at low risk of heart disease, having a hs-CRP may not be useful.

Conversely, if you already know you are at high risk, a hs-CRP will not provide new information. This test is most useful in people who are at moderate risk of heart disease. For these people, hs-CRP can add another data point to help doctors decide on the next steps, such as lifestyle changes or medication.

A high result tells your doctor that inflammation is happening in your body. However, the result cannot reveal where the inflammation is or what is causing it. Those answers will take more investigation. Your doctor will base the next steps on what is most likely the cause of the inflammation.

A CRP test involves a blood draw, usually from a vein in your arm. The procedure is quick and you may feel a slight pinch or sting. There is no special preparation for the test. Bruising can occur afterward.

Make sure your doctor knows about all the medications you take, including over-the-counter products. Some drugs can affect Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source  CRP test results. This includes statins, magnesium supplements, and nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Advil, Motrin). 

CRP levels go up when your body experiences inflammation Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source . This can be the result of an infection or some other inflammatory process.

A high CRP level means there is inflammation somewhere in your body. Finding and treating the cause of the inflammation can lower the level. Exercise and weight loss may also reduce the level.

CRP testing tells your doctor if there is inflammation happening in your body. It is a good marker of inflammation because the levels respond quickly to changes.

When doctors want to assess the risk of heart disease, they use a high sensitivity version of this test. The hs-CRP reports different results than the standard version. Both versions of the test involve a simple blood draw.