Gestational age and age at sampling influence metabolic profiles in premature infants.

To describe the influence that gestational age and chronological age have on amino acid and acylcarnitine profiles in an at-risk population of premature infants. Metabolic profiles (15 amino acids and 35 acylcarnitines) were obtained by using standard newborn techniques on infants born between 23 and 31 completed weeks of gestation. The profiles were drawn within the first 24 hours after birth and on approximately days 7, 28, and 42 of life or at discharge. A single, central, contract laboratory analyzed and managed the samples. We studied 995 patients; none was subsequently diagnosed with an inborn error of metabolism. Of the 3579 samples, there were 257 (7.2%) amino acid or acylcarnitine alerts reported in 214 infants (21.5% of infants studied). Both gestational age and postbirth chronological age significantly influenced the metabolic profile. Twenty-nine percent of infants at 23 to 26 weeks' gestational age had an abnormal metabolic profile compared with 17% of infants at 29 to 31 weeks' gestational age (P < .01). On the day of birth, 12% of the profiles were abnormal compared with 2% on day 28 (P < .01). The highest rate of abnormal values occurred on day 7 in the infants 23 to 26 weeks' gestational age (21%). These results demonstrate the complexity of understanding the impact of immaturity and disease on metabolic profiles used to screen for inborn errors of metabolism. Our data provide reference values for studies aimed at better understanding metabolism in preterm infants.