Lab tests and fibromyalgia

Doctors do not use lab tests to diagnose fibromyalgia. The results of lab tests done on people with fibromyalgia should be normal unless another condition is present.

You may have lab tests to rule out other diseases or to determine whether you have another disease in addition to fibromyalgia. Fibromyalgia may occur along with other joint and muscle (rheumatic) diseases, such as rheumatoid arthritis. Discovering these other conditions is important, because they may require different treatment.

If your doctor thinks that you may have another muscle or joint disease based on your symptoms, history, and physical exam, he or she may do any of the following tests:

• A complete blood count (CBC)
• An erythrocyte sedimentation rate (ESR) or a C-reactive protein (CRP) test to help identify diseases that cause inflammation, such as polymyalgia rheumatica
• A rheumatoid factor (RF) test to check for rheumatoid arthritis
• An antinuclear antibodies (ANA) test to check for certain conditions such as systemic lupus erythematosus (a condition that can affect the bones and skin and several other organs)
• Thyroid hormone tests to check for low or high thyroid gland activity. Thyroid problems can cause fatigue and muscle soreness.
• A blood calcium level test to check for a low calcium level, which can cause muscle cramps

The test results may show that you have a disease other than fibromyalgia. It is also possible that you have both fibromyalgia and another condition. Test results can be false-positive.

Doctors do not use these tests to diagnose fibromyalgia. You only need them if your medical history and physical exam suggest that you might have a condition other than fibromyalgia.