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

Abstract

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.

Figure 1

Predicted mean s[Cr] (dashed line) and upper 95th percentile (solid line) for each GA group. The underlying light gray lines depict plots of each study infant. (a) GA group 25–27 wk. (b) GA group 28–29 wk. (c) GA group 30–33 wk.