CRP and Diagnosis of Rheumatoid Arthritis

By  ,  Onlymyhealth editorial team
Dec 18, 2014
Quick Bites

  • In early stages, rheumatoid arthritis may be difficult to diagnose.
  • No single test can confirm that you have RA.
  • CRP levels in your blood can be part of a comprehensive diagnosis.
  • Your CRP levels should be normal if you don’t have RA.

Unlike osteoarthritis, which occurs because of the natural wear and tear of joints as one ages, rheumatoid arthritis (RA) is a result of your immune system attacking your joints. The cause for this occurrence is not fully understood. Rheumatoid arthritis is a type of arthritis that can affect anyone at any age. However, it’s more common in women and often first appears in middle age. Like any type of arthritis, swollen, painful joints mark the symptoms of RA.

Inflammation in Rheumatoid Arthritis

People with RA have painful joints because they’re inflamed. Inflammation is a natural process that occurs when your immune system attacks a foreign invader. Under a correctly working system, immune cells rush to an area of infection, like a cut, and go to work. This causes inflammation, redness, and pain in the particular area. RA-caused inflammation occurs because your immune system mistakes your joints for an invader.

Rheumatoid Arthritis

C-Reactive Protein (CRP) Test

CRP is a protein that’s produced by your liver and can be found in your blood. When inflammation occurs, CRP levels in your blood rise in response to it. For example, when you have an infection, the levels of CRP in your blood will rise. Accordingly, CRP levels that were high, will come down when the infection is under control.

Diagnosis of RA with CRP: No single test can confirm that you have RA, but measuring levels of CRP in your blood can be part of a comprehensive diagnosis. The criteria for diagnosing RA include:

  • other lab tests, such as scanning blood for an antibody called rheumatoid factor
  • the swelling and amount of pain in your joints
  • the duration of your symptoms

To do a CRP test, the lab professional will take a small sample of your blood. Your doctor will tell you beforehand if you need to fast or stop taking certain medications for getting this test done. After drawing your blood, the examiner will send it to a lab for testing, and your doctor will inform you of the results. There is almost no risk associated with having blood drawn for the CRP test.

Normal CRP Levels
If you don’t have any infections or chronic inflammatory illnesses such as RA, Crohn’s disease, or lupus, your CRP levels should be normal. Normal CRP levels are below 10.0 milligrams per deciliter (mg/dL). A standard CRP test often can’t even detect normal levels because they’re so low. To detect levels below 10.0 mg/dL, a high sensitivity CRP test can be done. This kind of test is performed to determine risk for cardiovascular disease. Levels of CRP over 3.0 mg/dL are thought to put you at a higher-than-average risk for heart disease.

CRP Test

Increased CRP Levels
To diagnose RA, your doctor will likely order a standard CRP test rather than a high-sensitivity test. Levels of CRP that can be detected with a standard test are considered advanced. Elevated levels of CRP are indicative of an inflammatory disease, but don’t confirm a definitive RA diagnosis.

CRP Levels and Response to Treatment

If you have been diagnosed with RA, occasional CRP tests would be ordered by your doctor. Your CRP levels are useful in suggesting if and how well your treatments are working. For instance, if your doctor has prescribed a new medication, they may test your CRP levels a few weeks later.

The medication is helping if your SRP levels are low. If they rise, your doctor will know that you’re having a flare up and may choose to try new treatments.

Evaluating CRP levels isn’t a precise method for diagnosing RA or the effectiveness of treatments. This is because CRP isn’t specific to RA. Elevated levels of CRP can indicate any type of infection or inflammatory disease. In fact, some studies have shown that up to 45 percent of patients had normal levels, yet were considered to have RA.

Image: Getty

Read more articles on Rheumatoid Arthritis.

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