C-reactive protein (CRP) is a protein that’s produced by your liver and can be found in your blood.

The levels of CRP in your blood will rise when you have an infection or major tissue injury. CRP levels in your blood also rise in response to inflammation. High CRP levels will fall when the underlying trigger is under control.

The autoimmune disease rheumatoid arthritis (RA) causes a lot of inflammation in addition to symptoms such as swollen and painful joints.

Keep reading to learn how CRP levels can be used to aid in the diagnosis and treatment of RA.

Your CRP levels should be within the normal range if you do not have any infections or chronic inflammatory conditions such as RA.

CRP is usually measured in milligrams of CRP per liter of blood (mg/L). Normal CRP levels are typically below 3.0 mg/L. Keep in mind that the normal reference range often varies between labs.

C-reactive protein level (in milligrams per liter of blood) in adultsWhat it means
Below 3.0Normal
3.0 – 10.0Slightly elevated, which may signify a variety of conditions such as pregnancy, the common cold, or gingivitis
10.0 – 100.0Moderately elevated, which signifies infection or an inflammatory condition such as rheumatoid arthritis (RA), Crohn’s disease, or lupus
100.0 – 500.0Elevated, which signifies infection, inflammation of the blood vessels, or major trauma
500.0 and aboveSeverely elevated, which signifies severe bacterial infection

A high-sensitivity CRP (hsCRP) test can detect levels below 10.0 mg/L. This kind of test is performed primarily to determine a person’s risk for heart disease.

hsCRP levels (in milligrams per liter of blood) in adultsWhat it means for heart disease risk
Below 1.0Low risk
1.0 – 3.0Moderate risk
3.0 – 10.0High risk

No single test can confirm that you have RA. However, measuring levels of CRP in your blood can be part of a comprehensive diagnosis. A doctor can use your CRP levels to track the degree of inflammation over time.

If you’re getting tested for RA, the doctor will likely order a standard CRP test rather than an hsCRP test.

To confirm a diagnosis of RA, the doctor will:

  • analyze results from other lab tests, such as the rheumatoid factor antibody test and cyclic citrullinated peptide (CCP) antibody test
  • assess levels of morning stiffness and the amount of swelling and pain in your joints
  • document the duration of your symptoms
  • examine X-rays of the hands and feet to check for erosions or bone damage

All you need to do for the CRP test is give a blood sample. Once your blood is drawn, it’ll go to a lab for testing. Your doctor will tell you the results, or you may be able to check them online.

There’s almost no risk associated with having blood drawn for the CRP test. However, reactions such as minor bruising or soreness are possible with any blood draw.

Once your doctor confirms an RA diagnosis, they may order occasional CRP tests. Your CRP levels are useful in indicating how well your treatments are working.

For instance, if you try a new medication, your doctor may test your CRP levels a few weeks after you start it.

If your levels have dropped, the medication is probably helping. If your CRP levels rise, your doctor will know that you’re having a flare-up. You may need to adjust your medications or try a new treatment.

Measuring CRP levels is not a perfect method for diagnosing RA or determining the effectiveness of a treatment. This is because CRP is not specific to RA. Elevated levels of CRP can indicate any type of infection or inflammatory condition.

On the other hand, some people with RA may have normal CRP levels. A study published in 2009 looked at databases of patients living with RA in Finland (Jyväskylä), and the United States (Nashville, Tennessee) over a period of 25 years.

Results showed that 44 to 58 percent of the patients, living in Finland and the United States, respectively, had normal CRP test results.

RA can affect anyone at any age, although it’s more common in women and often first appears in middle age.

If you have symptoms of the condition, such as joint pain, joint swelling, or nodules, speak with a doctor. They can use a variety of tests, including a CRP test, to confirm a diagnosis.

If it turns out that you have RA, your doctor can help you get started on a treatment plan that helps you manage your symptoms. Treatment may involve a combination of medications and natural remedies.