From the Guidelines
Laboratory tests for polymyalgia rheumatica (PMR) should include a basic dataset of rheumatoid factor and/or anti-cyclic citrullinated peptide antibodies (ACPA), C-reactive protein and/or erythrocyte sedimentation rate (ESR), blood count, glucose, creatinine, liver function tests, bone profile, and dipstick urinalysis, as recommended by the 2015 European League Against Rheumatism/American College of Rheumatology collaborative initiative 1. When evaluating a patient for PMR, it is essential to exclude mimicking conditions, such as giant cell arteritis or rheumatoid arthritis. The laboratory tests should be used to establish a baseline for monitoring therapy and to rule out other conditions.
- Key laboratory tests for PMR include:
- Inflammatory markers: ESR and CRP
- Autoantibody tests: rheumatoid factor and ACPA
- Blood count: to check for normocytic anemia
- Liver function tests: to exclude other conditions
- Bone profile: to assess calcium and alkaline phosphatase levels
- Dipstick urinalysis: to check for urinary abnormalities Additional tests, such as protein electrophoresis, thyroid-stimulating hormone (TSH), creatine kinase, and vitamin D, may be considered to exclude other conditions or to monitor disease activity 1. It is crucial to note that there is no single definitive test for PMR, and diagnosis is based on a combination of clinical symptoms, laboratory findings, and exclusion of other conditions 1.
From the Research
Lab Tests for Polymyalgia Rheumatica
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are commonly used laboratory tests to assess polymyalgia rheumatica (PMR) 2, 3
- ESR is considered a better indicator of clinical disease activity, except in patients who feel completely well at week 1 2
- CRP is a more sensitive indicator of current disease activity, but ESR is a superior predictor of relapse 3
- In some cases, PMR can be diagnosed with normal values of both ESR and CRP at the time of diagnosis 4
- Medical imaging, such as ultrasound and 18-fluorodeoxyglucose positron emission tomography associated with total body computed tomography (18-FDG PET/CT), can help confirm and clarify diagnosis, assess response to treatment, and evaluate for relapses 5, 4
Limitations of Lab Tests
- Blood tests often are inconclusive, and PMR symptoms overlap those of several other conditions 5
- "False positive" increases of ESR or CRP are rare, but can occur 2
- Normal ESR values at diagnosis are infrequent, but can occur in some patients 3
- CRP values at diagnosis are often elevated, even in patients with normal ESR 3