In a patient over 50 years old presenting with proximal muscle pain and stiffness suggestive of polymyalgia rheumatica, which baseline laboratory tests (e.g., erythrocyte sedimentation rate, C‑reactive protein, complete blood count, comprehensive metabolic panel, rheumatoid factor, anti‑cyclic citrullinated peptide antibodies, antinuclear antibody, thyroid function tests, vitamin D) should be ordered?

Laboratory Testing for Polymyalgia Rheumatica

Order ESR and/or CRP, complete blood count, comprehensive metabolic panel (glucose, creatinine, liver function tests), bone profile (calcium, alkaline phosphatase), urinalysis, rheumatoid factor and/or anti-CCP antibodies, creatine kinase, TSH, and vitamin D as your baseline laboratory dataset. 1

Core Inflammatory Markers (Essential)

• ESR and/or CRP are mandatory as inflammatory markers, with ESR being particularly valuable since high ESR (>40 mm/1st hour) predicts higher relapse rates and may guide your initial glucocorticoid dosing decisions. 2, 1
• Normal inflammatory markers represent an atypical presentation requiring specialist referral. 2

Baseline Tests Before Glucocorticoid Therapy (Essential)

• Complete blood count assesses for anemia and other causes of inflammation. 1
• Comprehensive metabolic panel including glucose, creatinine, and liver function tests establishes baseline before starting steroids. 3, 1
• Bone profile (calcium and alkaline phosphatase) assesses bone health before steroid therapy. 1
• Urinalysis excludes other inflammatory or infectious conditions. 1

Tests to Exclude Mimicking Conditions (Essential)

• Rheumatoid factor and/or anti-CCP antibodies exclude rheumatoid arthritis, which is a critical differential diagnosis. 1, 4
• Creatine kinase should be normal in PMR and helps differentiate from inflammatory myositis or myopathy. 1
• TSH rules out thyroid disorders presenting with similar symptoms. 1
• Vitamin D establishes baseline before glucocorticoid therapy. 1

Additional Testing Based on Clinical Context

• ANA and ANCA should be performed when other autoimmune conditions or vasculitis are suspected. 3, 1
• Protein electrophoresis excludes paraproteinemia mimicking PMR symptoms. 1
• Tuberculosis testing is necessary before considering immunosuppressive therapy or in high-risk patients. 3, 1
• Chest radiograph may be considered to exclude malignancy or other diagnoses. 3, 1

Critical Pitfalls to Avoid

• Do not skip rheumatoid factor/anti-CCP testing—progression from PMR to rheumatoid arthritis can occur, typically within 1-5 years of initial diagnosis. 4
• Do not rely solely on inflammatory markers for diagnosis; PMR remains primarily a clinical diagnosis supported by laboratory evidence. 1
• Atypical presentations requiring immediate specialist referral include: age <60 years, peripheral inflammatory arthritis, systemic symptoms, or low inflammatory markers. 3, 5

Comorbidity Assessment Before Treatment

Before initiating glucocorticoids, assess for hypertension, diabetes, glucose intolerance, cardiovascular disease, dyslipidemia, peptic ulcer disease, osteoporosis (particularly recent fractures), cataracts, glaucoma risk factors, and chronic/recurrent infections. 3 Female patients have higher risk of glucocorticoid side effects and require more vigilant monitoring. 3, 1