Fractional Excretion of Magnesium and Renal Concentrating Capacity in Refluxing Renal Units

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Abstract
To evaluate renal function in kidney units exposed to vesicoureteral reflux we quantified the fractional renal excretion of magnesium and the maximal renal concentrating capacity in 22 renal units of infants and children who presented with grade III to V vesicoureteral reflux on standard voiding cystourethrography. The lowest normal value for maximal concentrating capacity and the highest normal value for fractional excretion of magnesium were set at 800 mOsm. per kg. and 8 per cent, respectively. Concentrating capacity was abnormal in all 22 renal units and the excretion of magnesium was abnormal in 5. Failure of a renal unit to retain magnesium normally was always associated with an inability to concentrate urine. We conclude that in cases of vesicoureteral reflux function of the distal part of the nephron is the first to become abnormal and concentrating capacity is a more sensitive indication of dysfunction than fractional excretion of magnesium.