Neonatal urine insulin excretion and its relationship to infant hypoglycemia

Abstract

An intravenous glucose tolerance test was performed on 110 women during the third trimester of pregnancy in order to determine the status of their carbohydrate metabolism. The neonates from these women were followed closely in the nursery. Their urine was collected and the insulin/creatinine (I/C) level was measured on 332 daily urine samples. In addition, the neonates' fasting blood glucose levels were measured and the total daily caloric intake was determined. It was found that in the normal neonate there is a statistically significant positive correlation between the urine I/C level and the age of the neonate (r = 0.31; p < 0.0001). There is little change in the mean urine I/C level for the first four days of life. The mean urine I/C on days 1 to 4 was 35.4 μU per milligram whereas on days 5 to 8 it was 109.2 μU per milligram (p < 0.05). The increasing urine I/C level is significantly correlated with the increased caloric intake of the neonate (r = 0.35; p < 0.0001). There is a higher day 1 urine I/C level in infants who later develop hypoglycemia. Since this latter condition may produce permanent brain damage, it is suggested that a urine I/C screening test be performed on day 1 in order to identify the high-risk infant prior to the development of neonatal hypoglycemia.