Rates of creatinine and urea clearance in preterm infants on the 3 rd day after birth

Sir, In a recent paper published in the Archives (Sertel and Scopes, 1973), we reported the results of creatinine clearances in normal term infants. I have now studied rates of creatinine clearance in male preterm infants on the 3rd day of life. In the same infants the rates of urea clearance were measured. There were 11 male preterm infants studied on the 3rd day of life. Gestational age varied from 32 to 35 weeks, birthweight from 20 kg to 262 kg. All infants were bottle fed using a cow's milk formula (120 ml/kg per day). The procedure for collection of urine and capillary blood and for the determination of plasma and urine creatinine was the same as described in the previous paper. Plasma urea concentration was measured by the Barthelot reaction (Fawcett and Scott, 1960), and urine urea concentration by autoanalyser (Marsh, Fingerhut, and Kirsch, 1957). The summarized findings are presented in the Table. The creatinine clearance ranged from 10-6 to 23 1 mlfmin-per 1-73 m2, with a mean of 16 4 ml/min per 1 * 73 m2. The urea clearances ranged from 4-5 to 22 5 ml/min per 1 73 in2, with a mean of 11 4 ml/min per 1 73 in2. No correlation was found between gestational age and the creatinine or urea clearances in this study. Comparing the results with the rates of creatinine clearance of term infants found in our previous study, it appears that those of preterm infants are consistently lower. Plasma creatinine concentration in preterm infants measured on the 3rd day of life is lower than the level seen in term infants on day 1, but higher than that of term infants on day 6. Preterm infants have lower urinary creatinine concentrations than term infants on either day 1 or day 6. The values for urea clearance and plasma urea concentration on preterm infants are slightly lower than those of Dean and McCance (1947) in their study on term infants with meningomyelocele. They are also slightly lower than the values obtained by Gordon, Harrison, and McNamara (1942), but the infants in the latter series were all over one week of age. However, no distinction was made between small-for-dates and preterm infants in this latter study. The same criticism can be levelled against the 6 premature infants studied by Bamett et al. (1948). Thus the rates of creatinine and urea clearance in 11 normal preterm infants of less than 1 week of age were found to be even lower than those of normal term infants. The implications of these very low levels of rates of clearance are discussed in the previous paper.