To determine the population-based sensitivities and specificities of various inflammatory markers for the diagnosis of GCA.

Retrospective population-based cross-sectional study.

Patients who underwent temporal artery biopsy (TAB) from 01/01/1995 through 12/31/2019 in Olmsted County, Minnesota were identified using the Rochester Epidemiology Project (REP). Subjects were categorized as GCA or non-GCA using the 1990 American College of Rheumatology classification criteria for GCA.

Sensitivity and specificity of C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and platelets for a positive GCA diagnosis were calculated.

GCA diagnosis.

There were 553 patients who underwent TAB, 143 with GCA and 410 without GCA. Median age at time of TAB was 75 years (IQR 69-81) and 372 (67%) were female. Patients with GCA had higher CRP (91.1 vs 49.1 mg/L, P < .001), ESR (66.4 vs 52.0 mm/hr, P < .001), and platelets (370.5 vs 283.1 × 10⁹/L, P < .001) than patients in the non-GCA cohort. Sensitivity was 96% for CRP, 80% for ESR, and 49% for platelets. Specificity was 21% for CRP, 43% for ESR, and 79% for platelets. Combined ESR and CRP had a sensitivity of 77% and specificity of 54% while combined ESR, CRP, and platelets had a sensitivity of 41% and specificity of 84%. Normal inflammatory markers, including ESR, CRP, and platelets, were observed in 2 (3%) GCA patients.

This population-based study evaluated the performance of various inflammatory markers in the diagnosis of GCA. Inflammatory markers are helpful in the diagnosis of GCA, but normal values do not exclude the diagnosis.