Inulin clearance in the newborn infant: Relationship to gestational and postnatal age

Abstract

Thirty-eight healthy newborn infants with gestational ages ranging from 25 to 42 weeks were studied at 2 days to 9 weeks postnatal age to evaluate the rate of glomerular maturation after birth. Glomerular function was assessed by a constant infusion method for inulin clearance (Cin). Cin was nearly identical when measured by the traditional clearance method and by the constant infusion technique. The Cin of 22 infants 2-3 days old ranged from 0.6 to 17.9 ml/min and was directly related to gestational age (r = 0.81, P < 0.001). For 26 infants studied at 19 weeks of age, Cin, was directly proportional to conceptual (gestational and postnatal) age (r = 0.89, P < 0.001), and approximated that of infants of similar gestational age studied at 2 3 days of age. With the confirmation of the ease and accuracy with which Cin can be measured by the constant inulin infusion method, it should be possible to study glomerular filtration rate (GFR) under various clinical conditions, including very limited renal function. The lack of extrauterine acceleration of renal maturation which we have demonstrated may indicate an anatomic limitation in the first several months of life. © 1976 International Pediatric Research Foundation, Inc.