Question: Which Blood Tests Do Rheumatologists Order?
Also, when a patient has negative blood test results for usual arthritis indicators, but they have clinical symptoms such as pain, redness, warmth, swelling, and stiffness in their joints - do the negative labs preclude a diagnosis of arthritis?
Answer: Rheumatologists (doctors who specialize in arthritis and related conditions) typically order blood tests to help confirm or exclude a clinical diagnosis. For example, consider a patient who has a 3 month history of prolonged morning stiffness associated with pain and swelling of the wrists or hand. In this patient, the following blood tests might be ordered to help confirm a diagnosis of rheumatoid arthritis:
- Rheumatoid factor
- Anti-cyclic citrullinated peptide antibody
- Erythrocyte sedimentation rate
- C-reactive protein
The presence of a positive rheumatoid factor or CCP antibody in this patient would help confirm a diagnosis of rheumatoid arthritis. On the other hand, up to 30% of patients with rheumatoid arthritis may not have these antibodies, especially early in their disease. In addition, the presence of rheumatoid factor, especially at a low level, is not uncommon in patients who do not have and never will develop rheumatoid arthritis. The anti-CCP antibody is more likely to be associated with rheumatoid arthritis, so if a patient has a high level, the patient without typical manifestations of rheumatoid arthritis may be more likely to develop the disease.
The other two blood tests mentioned are the sedimentation rate and CRP. These blood tests measure inflammation and are typically elevated in patients with active rheumatoid arthritis. Normal levels do not rule out rheumatoid arthritis, but those patients may be less likely to develop joint damage compared to patients with high levels of inflammation. That's especially true of an elevated CRP.
An Antinuclear Antibody (ANA) test is important in our example patient to evaluate for systemic lupus erythematosus or SLE. While low levels of ANA are common in rheumatoid arthritis, high levels of ANA in the example patient suggest possible lupus, especially if the anti-CCP and rheumatoid factor are negative.
On subsequent visits, if the rheumatoid factor or anti-CCP are positive, they are usually not re-ordered. The sedimentation rate and CRP, however, are frequently ordered as they can help confirm (in addition to the patient's history and exam) whether the arthritis is active or in remission.
Answer provided by Scott J. Zashin, M.D., clinical assistant professor at University of Texas Southwestern Medical School, Division of Rheumatology, in Dallas, Texas. Dr. Zashin is also an attending physician at Presbyterian Hospitals of Dallas and Plano. He is a fellow of the American College of Physicians and the American College of Rheumatology and a member of the American Medical Association. Dr. Zashin is author of Arthritis Without Pain - The Miracle of Anti-TNF Blockers and co-author of Natural Arthritis Treatment.