Urinary β2-Microglobulin in Full-Term Newborns: Evidence for Proximal Tubular Dysfunction in Infants With Meconium-Stained Amniotic Fluid

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Urinary concentrations of β2-microglobulin (β2M) and creatinine were measured in normal term infants and in those born with meconium-stained amniotic fluid. None of the infants or their mothers had conditions known to modify β2M excretion. Measurements of β2M were made on urines collected by bagging; urines obtained from diapers were not satisfactory. Urinary β2M concentrations increased significantly (P < .02) in the normal infants from the first day (0.36 ± 0.29 mg/L: n = 29) to the third day (0.60 ± 0.43 mg/L: n = 21) postpartum. Compared with the normal infants, values for the infants with meconium-stained amniotic fluid were increased significantly on days 1 (1.64 ± 2.16 mg/L: n = 25: P < .005) and 3 (2.12 ± 2.04 mg/L: n = 23: P < .005). Levels exceeded two standard deviations above the normal mean in 12 of the 26 infants with meconium-stained amniotic fluid on postpartum day 1, and 12 of the 23 infants with meconium-stained amniotic fluid on day 3. Urinary creatinine levels were similar in both the normal infants and those with meconium-stained amniotic fluid. All infants with meconium-stained amniotic fluid with a one-minute Apgar score of 6 or less had an elevated urinary β2M concentration. The elevated levels of urinary β2M in infants with meconium-stained amniotic fluid indicate the existence of tubular dysfunction, probably mild acute tubular necrosis secondary to hypoxia.