Predictors of Gross Hematuria After SARS-CoV-2 mRNA Vaccination in Patients with IgA Nephropathy

Background There have been several reports of immunoglobulin A nephropathy (IgAN) patients with gross hematuria and acute deterioration of urinary findings and kidney function after severe acute respiratory syndrome coronavirus 2 mRNA vaccination. Recent case series studies have indicated a possible link between the status of urinary findings at the time of vaccination and the subsequent appearance of gross hematuria. In this study, we aimed to determine whether the status of prevaccination urinary findings was associated with postvaccination gross hematuria in patients already diagnosed with IgAN. Methods Outpatients with IgAN who had been followed up before vaccination were included. We analyzed the association between the remission of prevaccination microscopic hematuria (urine sediment <5 red blood cells/ high-power field) or proteinuria (<0.3 g/gCr) and postvaccination gross hematuria. Results A total of 417 Japanese patients with IgAN (median age, 51 years; 56% female; eGFR, 58 ml/min per 1.73 m2) were included. The frequency of gross hematuria after vaccination was higher in 20 of 123 patients (16.3%) with microscopic hematuria than in 5 of 294 patients (1.7%) without microscopic hematuria before vaccination (P < 0.001). There was no association between prevaccination proteinuria and postvaccination gross hematuria. After adjusting for potential confounders, such as sex (female), age (younger than 50 years), eGFR ($60 ml/min per 1.73 m2), and histories of tonsillectomy and corticosteroid therapy, prevaccination microscopic hematuria was still associated with postvaccination gross hematuria (odds ratio, 8.98; P < 0.001). As the severity of prevaccination microscopic hematuria increased, the incidence of postvaccination gross hematuria increased (P < 0.001). Conclusions Prevaccination microscopic hematuria in patients with IgAN is a major predictor of postvaccination gross hematuria, regardless of potential confounders, including previous treatments of IgAN.