Validation of the Southend Giant Cell Arteritis Probability Score in a Scottish single centre fast-track pathway
Abstract Objective To externally validate the Southend GCA Probability Score (GCAPS) in patients attending a GCA Fast-Track Pathway (GCA FTP) in NHS Lanarkshire. Methods Consecutive GCA FTP patients between November 2018 and December 2020 underwent GCAPS assessment as part of routine care. GCA diagnoses were supported by USS +/- TAB and confirmed at 6 months. Percentages of patients with GCA according to GCAPS risk group, performance of total GCAPS in distinguishing GCA/non-GCA final diagnoses, and test characteristics using different GCAPS binary cut-offs, were assessed. Associations between individual GCAPS components and GCA, and the value of USS and TAB in the diagnostic process, were also explored. Results 44/129 patients were diagnosed with GCA, including 0/41 GCAPS low risk patients (GCAPS <9), 3/40 medium risk (GCAPS 9–12), and 41/48 high risk (GCAPS >12). Overall performance of GCAPS in distinguishing GCA/non-GCA was excellent [ROC AUC 0.976 (95% CI 0.954–0.999)]. GCAPS cut-off ≥10 had 100.0% sensitivity and 67.1% specificity for GCA. GCAPS cut-off ≥13 had highest accuracy (91.5%), with 93.2% sensitivity and 90.6% specificity. Several individual GCAPS components were associated with GCA. Sensitivity of USS increased by ascending GCAPS risk group (nil, 33.3%, 90.2% respectively). TAB was diagnostically useful in cases where USS was inconclusive. Conclusion This is the first published study describing application of GCAPS outside the specialist centre where it was developed. Performance of GCAPS as a risk stratification tool was excellent. GCAPS may have additional value for screening GCA FTP referrals and guiding empirical glucocorticoid treatment.