Fractional excretion of Na++ < 1% is seen in

Fractional excretion of sodium (FeNa) less than 1% indicates the kidneys are appropriately conserving sodium in response to decreased renal perfusion, which is characteristic of pre-renal azotemia. In pre-renal states, intact renal tubular function avidly reabsorbs sodium and water to restore volume. In ATN and intrinsic renal failure, FeNa is typically greater than 2% due to tubular damage and inability to concentrate urine. Renal artery stenosis would also cause low FeNa (pre-renal pattern).