[Renal tubular function in preterm neonates]

Renal tubular function and functional changes in the preterm neonate are discussed. The proximal tubule has a limited capacity in preserving sodium, leading to a daily sodium need from 3 to 5 mEq/kg/day. The reabsorption of glucose, phosphate and amino acids is also low compared to older children but increases quickly for glucose and phosphate. At the level of the distal tubule, a temporary insensibility for aldosterone leads to a lowered sodium-potassium exchange. A limitation in acid excretion is present. Concentration capacity is restricted with a maximal urine osmolality of 360 mosm/liter. Despite this immature tubular function a glomerulotubular balance exists even in the preterm neonate. The kidneys are thus capable to preserve their homeostatic function.