A classification criteria-based gating strategy improves anti-neutrophil cytoplasmic antibody (ANCA) testing performance characteristics for the diagnosis of ANCA-associated vasculitis

The 2017 guideline-recommended gating strategy (RGS) for antineutrophil cytoplasmic antibody (ANCA) testing for ANCA-associated vasculitis (AAV) diagnosis has not been evaluated in Australia, and the optimal gating strategy remains unclear. We aimed to determine the performance characteristics of the RGS, a novel classification criteria-based gating strategy (CCGS) and the non-gated strategy (NGS) and estimated local cost-savings. We performed a retrospective analysis of ANCA tests at a tertiary referral laboratory (n=516, 19 AAV cases). NGS had 89.5% sensitivity, 98.2% specificity, 65.4% positive predictive value (PPV), 99.6% negative predictive value (NPV), likelihood ratios (LR+ and LR-) LR+49.4 and LR- 0.11. RGS had improved PPV (94.4%) and LR+ (444.7) and would have avoided 79.8% of ANCA tests. CCGS performed the same but would have avoided 85.9% of ANCA tests. No AAV cases were missed. CCGS would have yielded annual healthcare cost-savings of $A86 574. Implementing gating strategies may improve ANCA diagnostic performance for AAV, reduce testing volume and lead to significant healthcare cost-savings.