Objective: Simultanaeous testing for serum antineutrophil cytoplasmic antibodies (ANCA) by indirect immunofluorescence (IF) and by anti-proteinase-3 (PR3)/anti-myeloperoxidase (MPO) antibody assays may identify patients with PR3-ANCA or MPO-ANCA despite a negative IF (IF negative MPO/PR3-positive); however, the significance of this result is not clear. We sought to determine whether IF-negative MPO/PR3-positive results identified any cases of clinically meaningful systemic vasculitis at our institution. Methods: We conducted a retrospective analysis of all ANCA positive RPGN patients either by IF or ELISA identified at our institution from August 2017 - July 2018. Results: Out of 265 samples 45 were positive for both IF and ELISA, 220 were IF-negative. Among IF negative, 6 samples (2.7%), tested positive for MPO-ANCA or PR3-ANCA. Two IF-negative ELISA positive patients were subsequently diagnosed with ANCA-associated renal limited vasculitis. Two IF-negative ELISA-positive patients were previously diagnosed and treated for AAV, both with positive IF and antibody tests prior to treatment. 1 patient had SLE and 1 had inflammatory bowel disease. Mean age of patients 58±4, 56% were males and P-ANCA 67% and C-ANCA 33% only 1 pt had both C- ANCA AND P-ANCA patterns positive. Conclusion: In our study both IF and ELISA, ELISA positivity without a positive IF rarely led to a definite diagnosis of systemic vasculitis, and was more likely to occur in the context of a non-vasculitis inflammatory condition. Our results suggest that concurrent IF and MPO/PR3 testing may be important in preventing a missed diagnosis of new onset renal limited AAV.