Plasma urea and creatinine levels in very low birthweight (VLBW) infants.

Serial longitudinal measurements of plasma urea and creatinine were made in 12 VLBW infants (Birthweight 1500 mg) for 42 postnatal days. Plasma urea and creatinine were high and very variable during the first few days of life, both stabilising to lower levels by the second week. Plasma urea stabilised to very low levels (less than 2 mmol/l) below the accepted lower limit for infants, while plasma creatinine levels (50-70 mumol/l) were within the normal range. Both parameters may be of little help in estimating renal function during the perinatal period while plasma urea may be insensitive to changes in renal function in the post perinatal period. These characteristics of plasma urea and creatinine in VLBW infants must be borne in mind when these parameters are being used to assess renal function.