Plasma creatinine in the first month of life.

The creatinine-kinetics method of analysis was used to study the changes, during the first month of life, in plasma creatinine levels in 34 newborn infants receiving no treatment with drugs. Plasma creatinine values during the first 5 days of life ranged from 188 to 17 mumol/l. After day 5 plasma levels were fairly stable throughout the first month, with a mean value of 35 +/- 2 (range 12-62) mumol/l. Twenty-two infants receiving treatment with gentamicin-ampicillin-cloxacillin were also studied. Seven of them had raised plasma creatinine concentrations after day 5, well beyond the range of concentrations found for infants receiving no drugs. Plasma creatinine, measured by the kinetic method, appears to provide a useful index of renal function in the neonatal period.