What is a C-reactive protein (CRP) test?
A C-reactive protein (CRP) test measures the level of C-reactive protein — a protein made by your liver — in your blood. Your liver releases CRP into your bloodstream in response to inflammation.
When your body encounters an offending agent (like viruses, bacteria or toxic chemicals) or you have an injury, it activates your immune system. Your immune system sends out its first responders: inflammatory cells and cytokines.
These cells begin an inflammatory response to trap bacteria and other offending agents or start healing injured tissue. The result can be pain, swelling, bruising or redness. But inflammation also affects body systems you can’t see, such as your joints.
You normally have low levels of CRP in your blood. Moderately to severely elevated levels may be a sign of a serious infection or other inflammatory condition.
Why do healthcare providers perform CRP tests?
Healthcare providers typically order a C-reactive protein (CRP) test to help diagnose or rule out certain conditions, including:
- Severe bacterial infections, such as sepsis.
- Fungal infections.
- Osteomyelitis (infection of your bone).
- Inflammatory bowel disease (IBD).
- Some forms of arthritis.
- Autoimmune diseases, such as rheumatoid arthritis or lupus (systemic lupus erythematosus).
- Pelvic inflammatory disease (PID).
Providers also use CRP tests to monitor people after surgery or other invasive procedures to check for infection during their recovery period.
A CRP test alone can’t diagnose a condition or where the inflammation is in your body. Because of this, providers generally order additional tests if the CRP results show that you have inflammation.
When would I need a C-reactive protein (CRP) test?
Your healthcare provider may order a CRP test if you have symptoms of a serious bacterial infection, including:
- Rapid breathing (tachypnea).
- Rapid heart rate (tachycardia).
- Nausea and vomiting.
Your provider may also use CRP tests to monitor your treatment if you’ve already been diagnosed with an infection or a chronic inflammatory condition.
CRP levels increase and decrease depending on how much inflammation your body has. If your CRP levels go down, it's a sign that your treatment for the inflammation is working.
Who performs a CRP test?
A healthcare provider called a phlebotomist usually performs blood draws, but any healthcare provider who is trained in drawing blood can perform this task. The samples are sent to a lab where a medical laboratory scientist prepares the samples and performs the test on machines known as analyzers.
How do I prepare for a C-reactive protein (CRP) test?
Your healthcare provider will let you know what you need to do to prepare for a CRP test, but in most cases, you won’t need to do anything special to prepare for it (such as fasting before the test).
What should I expect during my CRP test?
You can expect to experience the following during a blood test, or blood draw:
- You’ll sit in a chair, and a healthcare provider will check your arms for an easily accessible vein. This is usually in the inner part of your arm on the other side of your elbow.
- Once they’ve located a vein, they’ll clean and disinfect the area.
- They’ll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
- After they insert the needle, a small amount of blood will collect in a test tube.
- Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
- They’ll place a bandage over the site, and you’ll be finished.
The entire procedure usually takes less than five minutes.
What should I expect after my CRP test?
After a healthcare provider has collected your blood sample, they’ll send it to a laboratory for testing. Once the test results are back, your healthcare provider will share the results with you.
What are the risks of a C-reactive protein (CRP) test?
Blood tests are a very common and essential part of medical testing and screening. There’s very little risk to having blood tests. You may have slight tenderness or a bruise at the site of the blood draw, but this usually resolves quickly.
Results and Follow-Up
When should I know the results of my C-reactive protein (CRP) test?
In most cases, you should have your CRP test results within one or two days, though it could take longer.
What type of results do you get for a C-reactive protein (CRP) test?
Blood test reports, including CRP blood test reports, usually provide the following information:
- The name of the blood test or what was measured in your blood.
- The number or measurement of your blood test result.
- The normal measurement range for that test.
- Information that indicates if your result is normal or abnormal or high or low.
What is the normal range for a CRP test?
Laboratories have different reference ranges for normal C-reactive protein (CRP) levels. When you get your blood test results back, there will be information that indicates what that lab’s normal CRP range is.
In general, the normal CRP level is less than 0.9 milligrams per deciliter (mg/dL).
Many factors can affect your CRP level. Minor CRP level elevation may be due to the following conditions or situations:
- Cigarette smoking.
- Common cold.
- Recent injury.
People assigned female at birth and elderly people have naturally higher levels of CRP.
If you have any questions about your results, be sure to ask your healthcare provider.
What does a high CRP level mean?
If you have a moderately to severely elevated CRP level, it probably means you have some type of inflammation. But a CRP test can’t show the cause of the inflammation or where it is in your body. Because of this, your healthcare provider will likely order additional tests if your result shows a high CRP level.
How high your CRP level is can mean different things.
A CRP test result of 1.0 to 10.0 milligrams per deciliter (mg/dL) is generally considered a moderately elevated level. This result may indicate any of the following conditions:
- Systemic inflammation from conditions such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) or other autoimmune conditions.
- Heart attack (myocardial infarction).
A CRP test result of more than 10 mg/dL is generally considered a marked elevation. This result may indicate any of the following conditions:
- Acute bacterial infections.
- Viral infections.
- Systemic vasculitis.
- Major injury (trauma).
A CRP test result of more than 50 mg/dL is generally considered severe elevation. Results over 50 mg/L are associated with acute bacterial infections about 90% of the time.
What does a low CRP level mean?
Since the normal CRP level is generally less than 0.9 mg/dL, there’s no such thing as a lower than normal CRP level.
If you previously had a high CRP result and now have a lower result, it likely means your inflammation is decreasing and/or your treatment for the inflammation is working.
Should I be concerned if my CRP level is abnormal?
If your CRP test results reveal that you have high levels of CRP, it doesn't necessarily mean that you have a medical condition that needs treatment, especially if they’re only slightly elevated. Several factors, such as smoking, recent injury and certain health conditions, can raise your CRP levels. There could’ve also been an error in the collection, transport or processing of the test.
If you have an abnormal result, your healthcare provider will discuss your results with you. They may order additional tests to determine the cause of your abnormal CRP levels.
A note from Cleveland Clinic
Seeing an abnormal test result can be stressful. Know that having an elevated CRP level doesn’t necessarily mean you have a medical condition and need treatment. Approximately 1 in 20 healthy people will have results outside of the normal range. Your healthcare provider will let you know if you need to have further tests to determine the cause of the abnormal level. Don’t be afraid to ask your provider questions. They’re available to help you.