Edsel B Ing, Gabriela Lahaie Luna, Andrew Toren, Royce Ing, John J Chen, Nitika Arora, Nurhan Torun, Otana A Jakpor, J Alexander Fraser, Felix J Tyndel, Arun NE Sundaram, Xinyang Liu, Cindy TY Lam, Vivek Patel, Ezekiel Weis, David Jordan, Steven Gilberg, Christian Pagnoux, Martin ten Hove

To develop and validate a diagnostic prediction model for patients with suspected giant cell arteritis (GCA). A retrospective review of records of consecutive adult patients undergoing temporal artery biopsy (TABx) for suspected GCA was conducted at seven university centers. The pathologic diagnosis was considered the final diagnosis. The predictor variables were age, gender, new onset headache, clinical temporal artery abnormality, jaw claudication, ischemic vision loss (VL), diplopia, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and platelet level. Multiple imputation was performed for missing data. Logistic regression was used to compare our models with the non-histologic American College of Rheumatology (ACR) GCA classification criteria. Internal validation was performed with 10-fold cross validation and bootstrap techniques. External validation was performed by geographic site. There were 530 complete TABx records: 397 were negative and 133 positive for GCA. Age, jaw claudication, VL, platelets, and log CRP were statistically significant predictors of positive TABx, whereas ESR, gender, headache, and temporal artery abnormality were not. The parsimonious model had a cross-validated bootstrap area under the receiver operating characteristic curve (AUROC) of 0.810 (95% CI =0.766-0.854), geographic external validation AUROC's in the range of 0.75-0.85, calibration pH-L of 0.812, sensitivity of 43.6%, and specificity of 95.2%, which outperformed the ACR criteria. Our prediction rule with calculator and nomogram aids in the triage of patients with suspected GCA and may decrease the need for TABx in select low-score at-risk subjects. However, misclassification remains a concern.