Would you pursue a kidney biopsy in a patient with stable stage 1 AKI, bland urine sediment, and a positive MPO titer without systemic signs of vasculitis?  

PR3-ANCA and MPO-ANCA are associated with substantially higher specificities and positive predictive values for ANCA-associated vasculitis (AAV) than the immunofluorescence patterns to which they usually correspond (C-ANCA and P-ANCA, respectively). However, false-positive results remain a concern.&...

In general, I would monitor the patient in the absence of hematuria or proteinuria, as necrotizing GN is unlikely. However, in ANCA, arteritis can occur without GN, though this presentation is uncommon.