Blood Tests for Rheumatoid Arthritis, part 2

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blood test for RAMany people with active RA have “normal” test results

In my last post, I posed the question: Is There a Blood Test for Rheumatoid Arthritis? I told you that the answer is yes – and no. I went on to describe the “yes” by summarizing four principal blood tests used in diagnosing Rheumatoid Arthritis. Now it is time to elaborate upon the “no.”

I found this startling:

You may already know that there is not a blood test to definitively measure Rheumatoid Arthritis. No blood test can be used to precisely diagnose RA in all patients. But just as importantly, there is not a test which can reliably gauge the degree of RA activity within a patient.

But, wait, it gets more interesting:

The most thorough study of the usefulness of these tests was a large study conducted in both Finland and Tennessee. Almost 2,500 patients were studied over a period of 25 years. The CRP, sed rate (ESR), and Rheumatoid factor (Rf) were all monitored.

Look at some of the results. ESR was normal in 45% (Finland) and 47% (Tennessee) of patients. CRP was normal in 44% and 58%. And all Rheumatoid factor (Rf) tests were negative in 38% and 37% of patients.

Why does this matter?

Doctors commonly use these three tests to “monitor disease activity.” That means they are looking to these numbers to show whether the disease is active and whether a patient’s current treatment plan is adequate. Some doctors are more reliant upon them than others. I have met one rheumatologist who says that he relies upon them completely.

So read this carefully:

Many people with RA experience plenty of active and damaging disease while one or all of these indicators are “normal.”

Here are a few cases in point:

  • “Sometimes also patients with rheumatoid arthritis have low CRP response in relation to the severity of the disease.” Axis-shield
  • “By the same token a normal sed rate is meaningless in a patient with known SLE if they are having symptoms of a flare.” (Sounds like this rheumatologist considers the lab test pretty useless to measure flares in Lupus.) Nathan Wei, MD, FACP, FACR
  • “However, a low CRP level does not always mean that there is no inflammation present. Levels of CRP may not be increased in persons with rheumatoid arthritis and lupus. The reason for this is not known.” University of Southern California
  • “Many people with active RA have inactive values of ESR/CRP and many with inactive RA have active values.” Journal of Rheum.
  • “Both ESR and CRP were normal in 33% and 42% of patients” in the large study mentioned earlier. Journal of Rheum. abstract

What is the bottom line?

Only a small percentage of people with RA actually had abnormal results to all three blood tests (ESR, CRP, and Rf) in the huge Finland / Tennessee study. “All 3 tests were abnormal in only 28% in Jyväskylä (Finland) and 23% in Nashville (Tennessee).” The authors of the study concluded: “Normal ESR, CRP, and RF are seen in a substantial proportion of patients with RA at this time.” Journal of Rheum. abstract

There is hope.

I had already spent many grueling hours researching for this series when I happened upon an article entitled The Many Myths of Erythrocyte Sedimentation Rate and C-Reactive Protein. I was thrilled to find a rheumatologist who holds the following viewpoint. “Learning when to ignore a test and when to rely on it lies at the heart of good medical care… It is, perhaps, time for more research about testing and measurement in clinical practice.” I recommend the article in the Journal of Rheumatology by Frederick Wolfe, M.D.

Recommended reading:

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Kelly Young. All rights reserved.

This entry was posted on Thursday, August 27th, 2009 at 7:00 am and is filed under Treating RA. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.


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