What is the accuracy of Erythrocyte Sedimentation Rate (ESR) in diagnosing Giant Cell Arteritis (GCA)?

Diagnostic Accuracy of ESR for Giant Cell Arteritis

ESR is a moderately sensitive but poorly specific test for diagnosing GCA, and should never be used alone to rule in or rule out the disease—an elevated ESR >50 mm/h has 87.5% sensitivity but requires additional clinical features, imaging, or temporal artery biopsy for definitive diagnosis. 1

Sensitivity and Specificity by ESR Threshold

The diagnostic accuracy of ESR varies significantly based on the cutoff value used:

• ESR >40 mm/h: Sensitivity 93.2%, negative likelihood ratio 0.18—this is the most sensitive threshold for screening 2
• ESR >50 mm/h: Sensitivity 87.5%, specificity 43.5%, negative likelihood ratio 0.27—this is the traditional cutoff with good sensitivity but poor specificity 1, 2
• ESR >60 mm/h: Sensitivity 70.7%, specificity 70.5%, positive likelihood ratio 5.77—provides more balanced diagnostic accuracy 2
• ESR >80 mm/h: Sensitivity 50.7%, specificity 81.8%, positive likelihood ratio 4.62 2
• ESR >100 mm/h: Sensitivity drops to approximately 50%, but specificity reaches 92.2% with positive likelihood ratio 3.11—highly specific but misses half of cases 2

Critical Limitations of ESR

A normal ESR does NOT exclude GCA. Between 4-15% of biopsy-proven GCA cases present with ESR <50 mm/h, and approximately 0.8-4% have both normal ESR and normal CRP at diagnosis 3, 4, 5. In one series of 177 biopsy-proven GCA cases, 7 patients (4%) had completely normal inflammatory markers 5.

Patients with GCA and normal ESR present differently:

• Lower frequency of headache and jaw claudication 4
• Higher proportion have polymyalgia rheumatica symptoms 5
• Less likely to have constitutional symptoms, anemia, or thrombocytosis 5

Comparative Performance: ESR vs CRP

CRP outperforms ESR as a diagnostic marker for GCA:

• CRP sensitivity: 90.1% (95% CI 76.3-96.3%), negative likelihood ratio 0.38 1
• CRP is elevated in >95% of GCA cases at diagnosis 6
• CRP <2.5 mg/dL has negative likelihood ratio 0.38, making GCA significantly less likely 6
• Recent evidence suggests ESR provides no additional diagnostic value beyond platelet count and CRP in sequential testing 7

Clinical Application Algorithm

When evaluating suspected GCA, interpret ESR in this context:

Features that UPGRADE suspicion despite normal/low ESR:

• Jaw claudication (positive LR 4.90) 1
• Limb claudication 2
• Temporal artery abnormalities on examination 6
• Anterior ischemic optic neuropathy 6, 2
• Platelet count >400 × 10³/μL 1, 2

Features that DOWNGRADE suspicion:

• Age ≤70 years (negative LR 0.48) 1
• ESR ≤40 mm/h (negative LR 0.18) 2
• Normal CRP (negative LR 0.40) 6

Critical Pitfalls

Do not wait for ESR results to make clinical decisions. Glucocorticoid treatment should be initiated immediately on strong clinical suspicion, as treatment can rapidly normalize inflammatory markers and affect biopsy results 1, 2. The 2020 JAMA Internal Medicine meta-analysis found that pretreatment ESR values showed better sensitivity than post-treatment values 1.

Confounding factors that artificially elevate ESR:

• Female sex (women have higher baseline ESR) 2
• Anemia 2
• Azotemia 2

No single test rules in or out GCA. The American College of Rheumatology emphasizes that temporal artery biopsy or appropriate imaging (vascular ultrasound, MRI, or PET) remains necessary for definitive diagnosis 1, 6. Even with highly suggestive clinical features and elevated ESR, histologic or imaging confirmation is required 1.