What blood work is recommended to diagnose polymyalgia rheumatica (PMR) in an older adult presenting with shoulder and hip pain and stiffness?

Blood Work for Polymyalgia Rheumatica Diagnosis

Order a core laboratory panel including ESR and/or CRP, rheumatoid factor and/or anti-CCP antibodies, complete blood count, comprehensive metabolic panel (glucose, creatinine, liver function tests), bone profile (calcium, alkaline phosphatase), and urinalysis to establish the diagnosis and exclude mimicking conditions. 1

Essential Initial Laboratory Tests

Inflammatory Markers (Required)

• ESR and/or CRP are essential for diagnosis, as inflammatory markers are elevated in over 90% of PMR patients 2
• ESR >40 mm/1st hour is particularly valuable, as high levels are associated with higher relapse rates and guide initial treatment intensity 1, 3
• Both markers should be obtained since they provide complementary information about systemic inflammation 1

Autoantibody Testing (Required to Exclude Mimics)

• Rheumatoid factor and/or anti-CCP antibodies must be checked to exclude rheumatoid arthritis, which is frequently misdiagnosed as PMR, particularly elderly-onset rheumatoid arthritis 1, 2
• These should be negative in true PMR 1

Complete Blood Count (Required)

• Obtain CBC to assess for anemia of inflammation and exclude other causes of symptoms 1
• This helps identify alternative diagnoses such as infections or malignancies 1

Metabolic Panel (Required Before Treatment)

• Glucose, creatinine, and liver function tests establish a baseline before initiating glucocorticoid therapy, which is the standard treatment 1
• This is critical since PMR patients are elderly and glucocorticoids will affect these parameters 1

Bone Health Assessment (Required)

• Bone profile including calcium and alkaline phosphatase assesses bone health before steroid therapy 1
• This is particularly important given the prolonged glucocorticoid exposure (typically 2-3 years) these patients will require 2

Urinalysis (Required)

• Urinalysis excludes other inflammatory or infectious conditions that may mimic PMR 1

Additional Recommended Tests

Muscle Enzyme Testing

• Creatine kinase should be normal in PMR, which differentiates it from inflammatory myositis 4, 1
• If CK is elevated, consider myopathy or myositis as alternative diagnoses 4

Exclude Other Conditions

• Protein electrophoresis excludes paraproteinemia which can mimic PMR symptoms 1
• TSH rules out thyroid disorders that may present with similar symptoms 1
• Vitamin D establishes a baseline before glucocorticoid therapy 1

Extended Testing for Atypical Presentations

When to Order Additional Autoantibodies

• ANA and ANCA testing should be considered when other autoimmune conditions are suspected based on atypical features 1
• These include peripheral inflammatory arthritis, systemic symptoms beyond typical PMR, age <60 years, or low inflammatory markers 1, 5

Pre-Treatment Screening

• Tuberculosis testing is necessary when immunosuppressive therapy is being considered or in high-risk patients 1
• Chest radiographs exclude malignancy, which can mimic PMR 1

Critical Diagnostic Pitfalls to Avoid

Common Mimics Requiring Specific Testing

• Elderly-onset rheumatoid arthritis is the most frequently misdiagnosed condition as PMR 2
• If peripheral joint synovitis develops or RF/anti-CCP become positive, the diagnosis should be reconsidered 1, 5
• Crystal arthropathies, septic arthritis, and soft tissue rheumatic disorders must be excluded if joint involvement is present 4

Interpreting Normal Inflammatory Markers

• While inflammatory markers are elevated in over 90% of cases, approximately 10% of PMR patients may have normal ESR/CRP 2
• In these atypical cases, consider specialist referral and imaging studies (ultrasound or MRI) to support the diagnosis 1, 5

Response to Steroids Is Not Diagnostic

• Do not use response to glucocorticoids as a defining diagnostic feature, as many conditions respond to steroids 6
• The diagnosis must be established based on clinical presentation and laboratory exclusion of mimics before treatment 6

Diagnostic Algorithm Summary

1. Initial assessment: Confirm bilateral shoulder pain, morning stiffness, age >50 years, and functional impairment 1
2. Core laboratory panel: Order ESR/CRP, RF/anti-CCP, CBC, metabolic panel, bone profile, urinalysis 1
3. Additional testing: Add CK, protein electrophoresis, TSH, vitamin D 1
4. Exclude mimics: If atypical features present, add ANA, ANCA, imaging studies 1
5. Therapeutic trial: Consider 12.5-25 mg prednisone equivalent daily after laboratory workup 1, 5