Rates of creatinine clearance in babies less than one week of age. Arch Dis Child

Rates of creatinine clearance in babies less than one week of age. Rates of creatinine clearance were measured in normal newborn babies by collecting a timed specimen of voided urine and estimating plasma creatinine. Each of the 17 babies had the estimation on day 1 and on day 6 of life. The mean rate on day 1 was 17 * 8 ml/minute per 1 * 73 m2, and there was a significant and systematic increase by day 6 when the mean rate was 36 4 ml/minute per 1 73 m2. The findings are important when assessing fluid requirements and drug dosage in the newborn. Although there are a few published individual measurements of creatinine clearance in babies less than a week old (Winberg, 1959, 3 cases; Dean and McCance, 1947, 8 cases with meningomyelocele), we have been unable to find any large series or any systematic examination of changes in the first days of life. Creatinine clearance is a not unreasonable measurement of glomeruler filtration rate in babies (Barnett and Vesterdal, 1953), and is therefore clearly an important measurement since it relates to fluid and electrolyte homoeostasis and rates of excretion of drugs. This paper reports plasma and urine creatinine concentrations and rates of creatinine clearance in 17 normal newborn babies, firstly on day 1 after birth and then again on day 6. Methods There were 17 babies investigated whose mothers had given permission for the study, 9 girls and 8 boys. Their gestational ages varied from 38 weeks to 41 weeks; birthweights from 2 600 to 4 260 kg, and all were clinically well. All were bottle fed using a cow's milk formula. The procedure was as follows. The baby was watched until he was seen to pass urine; this specimen was discarded. At this time a stop-watch was started and a urine collecting bag applied. All urine passed was then collected until an occasion when the baby was seen to void again. When this occurred the stop-watch was stopped, the urine bag was removed for measurement of volume of urine and for analysis, and a heel prick specimen of blood was obtained. If any urine was seen to leak, the urine collection was restarted and the bab