Urine solute excretion in growing low-birth-weight infants

Fifteen thriving low-birth-weight infants who weighed less than 1,950 gm at birth were randomly selected to study the urine solute excretion on two milk-based proprietary formulas, SMA or Formula 4. The results showed that urine oxmolality rose progressively with increasing caloric concentration and was 78, 111, and 163 mOsm/kg H2O on 67, 80, and 100 kCal/dl SMA, respectively. Formula 4 gave rise to significantly higher urine osmolality (133 mOsm/kg H2O) than SMA, when fed at the same caloric density of 67 kCal/dl. Although the dependence of urine solute excretion on dietary load was confirmed, the rapidly growing low-birth-weight infant appears to incorporate a larger portion of potential urine solute into growing tissues, than is the case in the term infant.