Urinary creatinine excretion in the newborn.

We measured the excretion rate of endogenous creatinine in 84 24-hour urine collections obtained from 60 term and preterm newborn infants between the 3rd and the 68th postnatal day, at postconceptional ages 28-42 weeks. The rate was positively correlated with weight, height, and postconceptional age but not with postnatal age; the strongest correlation was that with weight. When the rate was factored by weight it was constant across the range of values studied, with a median and logarithmic mean value of 90 mumol/kg/day (10 mg/kg/day) and a range (2 log SD) of 45-180 mumol/kg/day (5-20 mg/kg/day).