A diagnosis of polymyalgia rheumatica is based primarily on the patient's medical history, symptoms and a physical examination. No single test is available to definitively diagnose polymyalgia rheumatic; however, doctors often use lab tests to confirm a diagnosis or rule out other diagnoses or possible reasons for the patient's symptoms.
The most typical laboratory finding in people with polymyalgia rheumatica is an elevated erythrocyte sedimentation rate, commonly referred to as the "sed rate". This test measures inflammation by determining how quickly red blood cells fall to the bottom of a test tube of unclotted blood. Cells that descend too quickly (indicating an elevated sed rate) mean that the body is likely inflamed. While this sed rate measurement is a helpful diagnostic tool, it alone does not confirm polymyalgia rheumatica because inflamed tissue is a common symptom of many other forms of arthritis and rheumatologic diseases.
Before making a diagnosis of polymyalgia rheumatica, the doctor may order additional tests to help confirm the diagnosis. For example, the C-reactive protein test is another common means of measuring inflammation. There is also a common test for rheumatoid factor, an antibody (a protein made by the immune system) that is sometimes found in the blood of people with rheumatoid arthritis. While polymyalgia rheumatica and rheumatoid arthritis share many symptoms, those with polymyalgia rheumatica rarely test positive for rheumatoid factor. Therefore, a positive rheumatoid factor might suggest a diagnosis of rheumatoid arthritis instead of polymyalgia rheumatica.