Measurement of the urinary lactate : creatinine ratio for the early identification of newborn infants at risk for hypoxic-ischemic encephalopathy

Background Newborn infants with perinatal asphyxia are prone to the develop ment of hypoxic-ischemic encephalopathy. There are no reliable methods For identifying infants at risk for this disorder. Methods We measured the ratio of lactate to creatinine in urine by proton n uclear magnetic resonance spectroscopy within 6 hours and again 48 to 72 ho urs after birth in 58 normal infants and 40 infants with asphyxia. The resu lts were correlated with the subsequent presence or absence of hypoxic-isch emic encephalopathy. Results Hypoxic-ischemic encephalopathy did not develop in any of the norma l newborns but did develop in 16 of the 40 newborns with asphyxia. Within s ix hours after birth, the mean (+/-SD) ratio of urinary lactate to creatini ne was 16.75+/-27.38 in the infants who subsequently had hypoxic-ischemic e ncephalopathy, as compared with 0.09+/-0.02 in the normal infants (P<0.001) and 0.19+/-0.12 in the infants with asphyxia in whom hypoxic-ischemic ence phalopathy did not develop (P<0.001). A ratio of 0.64 or higher within six hours after birth had a sensitivity of 94 percent and a specificity of 100 percent for predicting the development of hypoxic-ischemic encephalopathy. The sensitivity and specificity of measurements obtained 48 to 72 hours aft er birth were much lower. The mean ratio of urinary lactate to creatinine w as significantly higher in the infants who had adverse outcomes at one year (25.36+/-32.02) than in the infants with favorable outcomes (0.63+/-1.50) (P<0.001). Conclusions Measurement of the urinary lactate:creatinine ratio soon after birth may help identify infants at high risk for hypoxic-ischemic encephalo pathy. (N Engl J Med 1999;341:328-35.) (C) 1999, Massachusetts Medical Soci ety.