Urinary thiobarbituric acid-reacting substances as potential biomarkers of intrauterine hypoxia.

BACKGROUND Currently available clinical tools cannot accurately identify the extent of perinatal hypoxic injuries. During hypoxia, reactive oxygen species cause lipid peroxidation of cell membranes, yielding oxidation products that constitute thiobarbituric acid-reacting substances (TBARS). OBJECTIVE To see if the concentrations of TBARS excreted in urine would be elevated during the first day of life in term and preterm infants following chronic hypoxia or acute asphyxia. DESIGN Thiobarbituric acid-reacting substances levels were measured by a spectrophotometric assay in urine samples collected from term and near-term (>/= 34 weeks gestation, n = 22), and preterm (<34 weeks gestation, n = 52) infants on the first day of life. PATIENTS Infants were admitted to the St Peter's University Hospital (New Brunswick, NJ) neonatal intensive care unit from July 1997 to January 1999. Acute asphyxia was defined as umbilical cord blood pH values less than 7.05, or Apgar scores of less than 5 at 5 minutes. Chronic hypoxia was defined as intrauterine growth retardation or low birth weight (small for gestational age) associated with pregnancy-induced hypertension or reversal of umbilical arterial blood flow. RESULTS Among term infants, urinary TBARS levels were significantly increased following acute asphyxia (P =.02). Levels of TBARS also tended to be elevated following chronic hypoxia. Urinary TBARS levels in term infants tended to be increased in those requiring mechanical ventilation (P =.05) or delivery room resuscitation (P =.15), as well as in those passing intrauterine meconium (P =.13) or having clinical evidence of hypoxic-ischemic encephalopathy (P =.24). CONCLUSIONS The results show a correlation between elevated urinary TBARS levels in term and near-term infants, and perinatal hypoxia (as determined by low Apgar scores or umbilical cord blood acidosis). We speculate that TBARS concentrations may be useful as a biomarker for perinatal hypoxic injury in newborns. Further studies are needed to determine whether elevations in TBARS levels are better predictors of the extent of hypoxic injury than existing markers.