Patients with immunoglobulin A nephropathy (IgAN) who present with mild to moderate proteinuria and normal renal function are assumed to have excellent short-term renal prognosis, but the long-term prognosis is uncertain.

Patients were selected from the Norwegian Kidney Biopsy Registry based on the following criteria: diagnostic renal biopsy performed in the period 1988–99, with estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m² and proteinuria <1 g/24 h at the time of biopsy. Patients were invited for a nephrological examination with a review of medical history and investigation of blood pressure, urinary findings and eGFR.

A total of 145 patients attended the examination, performed by the first author, after a median of 22 (interquartile range 19–25) years after diagnosis. At the examination, 27 patients (18.6%) had a ≥50% decrease in GFR, of whom 4 (2.8%) had developed end-stage renal disease (ESRD). The mean duration from renal biopsy to ≥ 50% decrease in GFR was 17.3 ± 5.1 years in our cohort. Clinical remission was observed in 42 (29.0%) patients. Renal biopsies were re-examined utilizing the Oxford classification criteria. Mesangial hypercellularity was found in 12.3%, endocapillary proliferation was detected in 10.7% and segmental glomerulosclerosis was observed in 23.8%. All biopsies were scored as T0 (tubular atrophy in < 25% of the cortical area). None of the clinical or histopathological variables recorded at the time of biopsy could identify patients with progressive disease. Cumulative risks of ≥50% decrease in eGFR were 2.1% after 10 years, 4.1% after 15 years, 13.9% after 20 years and 24.7% after 25 years.

We have shown that 18.6% of patients with assumed benign IgAN had progressive disease after a median duration of 22 years and that these patients could not be predicted at the time of biopsy. Our study demonstrates that an extended follow-up period is needed when assessing prognosis in this group of patients.