Know the basics
What is C-reactive protein test?
A C-reactive protein (CRP) test is a blood test that measures the amount of a protein called C-reactive protein in your blood. C-reactive protein measures general levels of inflammation in your body.
High levels of CRP are caused by infections and many long-term diseases. But a CRP test cannot show where the inflammation is located or what is causing it. Other tests are needed to find the cause and location of the inflammation.
Why is C-reactive protein test performed?
The CRP test is a general test to check for inflammation in the body. It is not a specific test. That means it can reveal that you have inflammation somewhere in your body, but it cannot pinpoint the exact location.
Your doctor may order this test to:
- Check for flare-ups of inflammatory diseases such as rheumatoid arthritis, lupus, or vasculitis.
- Determine if anti-inflammatory medicine is working to treat a disease or condition.
Things to know before
What should I know before receiving C-reactive protein test?
A low CRP level does not always mean that there is no inflammation present. Levels of CRP may not be increased in people with rheumatoid arthritis and lupus. The reason for this is unknown.
A more sensitive CRP test, called a high-sensitivity C-reactive protein (hs-CRP) assay, is available to determine a person’s risk for heart disease. Many consider a high CRP level to be a risk factor for heart disease. However, it is not known whether CRP is merely a sign of cardiovascular disease or if it actually plays a role in causing heart problems.
Know what happens
How to prepare for C-reactive protein test?
There are no special preparations for either a standard CRP test or an hs-CRP test. However, if your blood is being drawn for other tests, as well, you may need to fast or follow other instructions. Ask your doctor if you’re having other tests at the same time.
Some medications can affect your CRP level. Tell your doctor about any medications you take.
What happens during C-reactive protein test?
The health professional taking a sample of your blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure on the site and then put on a bandage.
What happens after C-reactive protein test?
An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
If you have any questions about the C-reactive protein test, please consult with your doctor to better understand your instructions.
Understand the results
What do my results mean?
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Results are usually available within 24 hours.
|C-reactive protein (CRP)|
|Normal:||Less than 1.0 milligram per deciliter (mg/dL) or less than 10 milligrams per liter (mg/L)|
Any condition that results in sudden or severe inflammation may increase your CRP levels.
Some medicines may decrease your CRP levels.
Many conditions can change CRP levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.
High-sensitivity C-reactive protein (hs-CRP) levels
High-sensitivity C-reactive protein (hs-CRP) measures very low amounts of CRP in the blood. This test may help find your risk of heart problems, especially when it is considered along with other risk factors such as cholesterol, age, blood pressure, and smoking. It may be done to find out if you have an increased chance of having a sudden heart problem, such as a heart attack or stroke. But the connection between high CRP levels and heart disease risk is not understood very well.
|High-sensitivity C-reactive protein (hs-CRP) level|
|Normal:||Less than 0.1 mg/dL or less than 1 mg/L|
|hs-CRP level and heart disease risk|
|Less than 1.0 mg/L||Low risk|
|1.0 to 3.0 mg/L||Average risk|
|More than 3.0 mg/L||High risk|
Depending on the laboratory and hospital, the normal range for C-reactive protein test may vary. Please discuss with your doctor any questions you may have about your test results.
Hello Health Group does not provide medical advice, diagnosis or treatment.
Review Date: January 4, 2017 | Last Modified: January 4, 2017
Ferri, Fred. Ferri’s Netter Patient Advisor. Philadelphia, PA: Saunders / Elsevier, 2012. Download version.
Porter, R. S., Kaplan, J. L., Homeier, B. P., & Albert, R. K. (2009). The Merck manual home health handbook. Whitehouse Station, NJ, Merck Research Laboratories. Page 1856.