Serum creatinine concentration in very-low-birth-weight infants from birth to 34-36 wk postmenstrual age.

BACKGROUND: Serum creatinine (s[Cr]) reference ranges for very-low-birth-weight (VLBW) infants must account for physiologic changes in the first months of life.

METHODS: We retrospectively identified a sample of 218 appropriate-for-gestational age (GA) VLBW infants without risk factors for renal impairment, and classified into one of three GA groups: 25-27, 28-29, and 30-33 wk. We observed three phases of s[Cr] change (initial, decline, and equilibrium), whose characteristics varied by GA group. We used mixed-effects regression models to estimate mean and upper 95th prediction interval of s[Cr] for each GA group from birth to 34-36 wk post menstrual age (PMA).

RESULTS: In phase I, s[Cr] increased after birth, then returned slowly to baseline. The duration of phase I and the magnitude of s[Cr] rise decreased with increasing GA. In phase II, s[Cr] declined abruptly at a rate that increased with GA. A gradual transition to phase III, a steady-state equilibrium with similar s[Cr] among GA groups, began at approximately 34-36 wk PMA. We constructed GA group-specific nomograms depicting s[Cr] behaviour across the three phases.

CONCLUSION: The reference ranges derived from a sample of infants without risk factors for renal impairment provide a context for quantitative interpretation of s[Cr] trends in VLBW infants.