Ayşe ARSLAN, Alper TOGAY
The Eurasian Journal of Medicine - 2026;58(4):1-5
Background: Current guidelines recommend myeloperoxidase (MPO)- and proteinase 3 (PR3)-based immunoassays as the primary approach for antineutrophil cytoplasmic antibody (ANCA) testing, while indirect immunofluorescence (IIF) is reserved for selected clinical contexts. However, real-world data regarding concordance and workflow implications of these approaches remain limited. Methods: In this retrospective laboratory-based study, ANCA results from 8976 consecutive patients evaluated in a high-volume tertiary laboratory were analyzed. Indirect immunofluorescence patterns and MPO/PR3 reactivity were assessed simultaneously using an integrated IIF-based platform. Concordance between IIF patterns and antigen-specific reactivity was evaluated, and retrospective workflow simulations were performed to estimate the effects of MPO/PR3-first and IIF-first testing approaches on laboratory test utilization. Results: Overall IIF positivity was observed in 589 patients (6.56%), whereas MPO and/or PR3 reactivity was detected in 307 patients (3.42%; 95% CI: 3.06-3.82%). Among IIF-positive patients, 438 (74.4%) showed no detectable MPO or PR3 reactivity, while 156 antigen-reactive patients (50.8%; 95% CI: 45.1-56.5%) showed no identifiable IIF reactivity. Retrospective workflow simulations suggested that an MPO/PR3-first approach would substantially reduce IIF testing volume, whereas an IIF-first strategy would markedly decrease antigen-specific testing volume. However, each approach was associated with distinct discordance patterns between IIF and MPO/PR3 reactivity within the study cohort. Conclusion: Substantial discordance was observed between IIF patterns and MPO/PR3 reactivity. The findings reflect laboratory concordance and workflow characteristics rather than true clinical diagnostic performance, and the clinical significance of discordant findings requires further evaluation in clinically characterized cohorts.
