Clinical value of renal biopsy in patients with asymptomatic microscopic hematuria with and without low-grade proteinuria

The decision whether to perform renal biopsy on patients with persistent asymptomatic microscopic hematuria (AMH) with and without low-grade proteinuria (LGP) remains controversial as, although often diagnostic, the information gained seldom alters clinical management. Our study investigates the clinical value of renal biopsy in patients with isolated AMH versus those with AMH and LGP.Between 1996 and 2002, we identified 89 patients with AMH and 46 with AMH and LGP. The patients were asymptomatic, free from systemic illness, had a sterile urine, normal serum creatinine, normal renal and bladder ultrasound, less than 2.5 g proteinuria/day, underwent successful renal biopsy and were followed-up for a mean period of 46 +/- 12 months.In patients with isolated AMH, thin basement membrane nephropathy (TBMN) was diagnosed in 43%, IgA nephropathy in 20%, minor abnormalities in 19% and normal biopsies in 18%. In patients with AMH and LGP, IgA nephropathy was diagnosed in 46%, other major nephropathies in 26%, minor abnormalities in 17%, TBMN in 7% and normal biopsies in 4%. At follow-up, 32% of AMH patients and 38% of AMH with LGP patients had a GFR of less than 90 ml/min and 36% and 56%, respectively were hypertensive.The results support the current consensus that routine renal biopsy is not indicated for isolated AMH but suggest that biopsy is indicated for AMH and LGP identifying major and potentially progressive nephropathies in 70% of patients, who should be managed by specialist nephrologists.