Patients who have only recurrent episodes of gross hematuria seem to be at less risk than those with persistent microscopic hematuria and proteinuria [1,23] . Why this might occur is not clear.
Acute renal failure with gross hematuria — Acute renal failure can occur during episodes of gross hematuria [24-26] . Renal biopsy in these patients reveals mesangial proliferation and segmental crescents in a small proportion of glomeruli (usually less than 25 percent) [24,26] . These findings are insufficient to account for the acute renal failure, which has been ascribed to tubular obstruction by red cell casts . However, the most common histologic lesion is acute tubular necrosis, which may be induced by the iron released from lysed red cells in the tubules  .

This form of acute renal failure is generally a benign complication; the serum creatinine concentration most commonly returns to baseline levels within several weeks to months, even if dialysis is temporarily required [24] . However, incomplete recovery of renal function has been described in up to 25 percent of affected patients [27] .

Histologic predictors of progression — Although clinical features appear to be stronger prognostic indicators [18] , certain findings on renal biopsy have been associated with an increased risk of progressive disease. These include glomerulosclerosis, tubular atrophy, interstitial fibrosis, immune deposits in the capillary loops as well as the mesangium, vascular disease, and crescent formation  .
Several schema for classifying renal biopsy findings have been described that appear to correlate with prognosis; in multivariate analyses, the extent of glomerulosclerosis and tubulointerstitial disease are most commonly associated with a poor prognosis . These indicators are typical of most glomerular diseases. (See "Secondary factors and progression of chronic kidney disease", section on Tubulointerstitial disease).
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