Plasma and urine carnitine levels during development.

Plasma and urine free carnitine concentration during human development was evaluated. A positive correlation was found between plasma level and body weight in premature neonates weighting between 1.15 and 1.80 kg. In full terms newborns, the free carnitine concentration (mean +/- S.E., 31.2 +/- 2.5 nmoles/ml) is similar to that of premature babies with 33 to 36 wk of gestational age (37.5 +/- 3.1 nmoles/ml) but significantly lower than that of premature babies aged 30 to 33 wk of gestation (43.0 +/- 5.6 nmoles/ml). In the first 2 wk of life, free carnitine level showed a good correlation with age in the full-term newborns. Adult levels are reached by the end of the first 6 months. no sex related difference was observed in any of the different groups during growth. Urinary excretion of free carnitine per day is significantly lower in infants 0 to 3 years old (mean +/- S.E., 15.5 +/- 1.8 mumoles/24 hr) and in children 3 to 10 years old (115.3 +/- 11.4 mumoles/24 hr) than in subjects ranging in age from 22 to 70 years (216 +/- 20.6 mumoles/24 hr). We found no difference between day- and nighttime urinary excretion in newborns and infants.