Unclassifiable repeated antineutrophil cytoplasmic antibody (ANCA) positivity in diseases other than ANCA-associated vasculitis.

Overall, regardless of category, the common diseases with unclassifiable repeated ANCA were chronic kidney disease followed by interstitial lung disease and vasculitis undetermined. Thus, we carefully suggest that physicians should pay more attention to the development of AAV or vasculitis other than AAV and, furthermore, kidneys and lungs should be monitored regularly and closely in patients with unclassifiable repeated ANCA.