What blood tests are commonly ordered to diagnose and monitor arthritis?

Question: What blood tests are commonly ordered to diagnose and monitor arthritis?

How important are blood tests in diagnosing arthritis? What blood tests are commonly ordered and what do they tell a rheumatologist about an individual patient?

When a patient has negative blood test results for the arthritis indicators, but have all the clinical symptoms such as pain, redness, warmth, swelling, and stiffness in their joints - do the negative labs preclude a diagnosis of arthritis?

What is the determining factor in what tests are ordered and how often?

Answer: Rheumatologists (doctors who specialize in the treatment of arthritis) 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 "RF"

anti-cyclic citrullined peptide "CCP"

erythrocyte sedimentation rate "ESR"

C-reactive protein "CRP"

The presence of a positive RF or CCP in this patient would help confirm a diagnosis of rheumatoid arthritis (RA). On the other hand, up to 30 % of patients with RA may not have these antibodies, especially early in their disease. In addition, the presence of a RF, especially at a low level is not uncommon in patients who do not have, and never will develop RA. The anti-CCP antibody is more likely to be associated with RA, so if elevated at a high level, the patient without typical manifestations of RA may be more likely to develop the disease.

The other two blood tests mentioned are the ESR and CRP. These blood tests measure inflammation and are typically elevated in patients with active RA. Normal levels do not rule out RA, but those patients may be less likely to develop damage in their joints than patients with high levels of inflammation, especially an elevated CRP.

An anti-nuclear antibody (ANA) is an important test in our example patient to evaluate for systemic lupus erythematosus or SLE. While low levels of ANA are common in RA, high levels of ANA in this example patient may indicate possible lupus, especially if the CCP and RF are negative.

Finally, on subsequent visits, the RF and CCP are not typically re-ordered if positive. On the other hand, the ESR and CRP are frequently ordered as they can help confirm (in addition to the patients 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. The book is a must-have for anyone on one of the biologic drugs (Enbrel, Remicade, Humira) or considering the biologic drugs. Read my review of the book.