ANCA testing strategies: A single centre experience over the past decade in a large teaching hospital in the Netherlands

Objectives In 2017 a new consensus for antineutrophil cytoplasmic antibody (ANCA) testing was published, based on data from tertiary referral centres for ANCA-associated vasculitis (AAV). AAV-prevalence in their tested population was relatively high. We analysed how the consensus approach performs in a large teaching hospital and tailored it to secondary care settings with lower patient prevalences in their population. Methods Patients screened for ANCA between 2012–2023 were included; clinical data were retrospectively collected. Indirect immunofluorescence (IIF) was performed using EUROPLUS TM Granulocyte Mosaic 25 IIF. MPO/PR3 was detected by ImmunoCAP®250. Statistical analyses were performed in R. Results 286/5518 (5.2%) patients tested for ANCA were positive: 63% had no AAV. Non-AAV patients often had other autoimmune diseases, malignancies, infections or used specific drugs. IIF and ELISA as first test showed good negative predictive values. ELISA as first test showed higher positive predictive value and specificity; performing a second test increased specificity. ANCA concentrations were higher in AAV than non-AAV, but ranges were wide. Conclusion The majority of ANCA-positive patients did not have AAV. In our secondary care setting, ELISA performs best as first test to rule out and to rule in AAV. A second test should be considered with high clinical suspicion and a negative first test, or with low antibody concentrations, following the consensus. Additionally, we propose a second test when there is clinical doubt and a positive first test. This increases specificity and PPV, reducing false positives, which is especially relevant in secondary care settings.