Effect on renal net acid excretion of various mineral contents in three lots of a common pre-term formula.

Three common lots (A, B, C) of a common formula for pre-term infants, which contained unintended, high differences in mineral contents were fed consecutively in a neonatal unit. In each feeding period parameters of calcium-phosphorus and acid-base metabolism were determined prospectively. Infants fed lot C showed unexpectedly high renal net acid excretion. In order to discover the origin of this different renal net acid excretion, the urinary concentration of further electrolytes, sulfate, urea and organic acids were determined retrospectively in three randomly selected groups with 10 pre-term infants each. Infants fed lot C showed a higher renal net acid excretion (2.97 mmol/kg per day) than infants fed lot A (1.75 mmol/kg per day) or lot B (1.72 mmol/kg per day). Based on the data of mineral and nitrogen intake and the urinary values of all main ions and urea it is assumed that the increased renal acid load in infants fed lot C is due to the additive effect of different mineral concentrations resulting in a low "alkali excess" (Na + K - Cl) of lot C and a decreased protein assimilation. The production of infant formulas for prematures should be more closely monitored to avoid marked deviation of the mineral contents in individual lots from the concentrations shown on the label.