Gross hematuria after COVID-19 mRNA vaccination and kidney function trajectory in IgA nephropathy

Gross hematuria (GH) following COVID-19 mRNA vaccination has been increasingly reported in patients with IgA nephropathy (IgAN). This study assessed the effect of post-vaccination GH on kidney function. A total of 441 Japanese outpatients with biopsy-confirmed IgAN (median age: 51 years; 56% female; baseline eGFR: 57 mL/min/1.73 m²) were classified into three groups: unvaccinated (n = 25), vaccinated without GH (n = 391), and vaccinated with GH (n = 25). Kidney function was evaluated at approximately 1 year (midpoint) and 2 years (endpoint) after baseline. The annual eGFR change (ΔeGFR: mL/min/1.73 m²/year) at midpoint was - 1.16, - 1.03, and - 2.50, respectively. The GH group showed a significantly greater decline compared to the non-GH group (p = 0.015), and GH was significantly associated with greater eGFR decline at midpoint (odds ratio: 2.97, p = 0.038). At the endpoint, the ΔeGFR was - 0.45, - 1.93, and - 1.72, with no significant differences among the groups (p = 0.773). In this cohort, GH after vaccination was observed to be associated with a greater short-term decline in kidney function, although the retrospective design precludes establishing causality.