Plasma creatinine rises dramatically in the first 48 hours of life in preterm infants

Objective. Published data show that plasma creatinine falls steadily during the first 28 days of life and that creatinine levels in the neonatal perio d are higher in more premature infants. However, the best reference data co mmence on day 2 of life. The objective of this study was to document how pl asma creatinine changes in the first 48 hours of life and to examine the re ason for the apparently high levels of creatinine in preterm infants, compa red with maternal levels. Design. A prospective observational study on a regional neonatal intensive care unit. Patients. A total of 42 preterm infants, mean gestational age of 29.4 weeks (range: 23-35), mean birth weight of 1.42 kg (.55-2.77), divided into 4 ge station groups: 23 to 26 weeks (n = 9), 27 to 29 weeks (n = 13), 30 to 32 w eeks (n = 12), and 33 to 35 weeks (n = 8). Interventions. Measurement of plasma creatinine and urea concentration in c ord blood and in serial samples taken for routine arterial blood gas analys is. Outcome Measurements. Changes in creatinine concentration with time and rel ationship to gestational age, birth weight, and illness severity. Results. Mean creatinine at birth was 73 mu mol/L (95% confidence interval [CI]: 68-79 mmol/L). Plasma creatinine rose significantly over the first 48 hours. Mean peak creatinine in the most preterm infants (23-26 weeks) was 221 mu mol/L (CI: 195-247 mu mol/L). Peak plasma creatinine was inversely r elated to gestation (Spearman's coefficient: 2. 73) and birth weight (Spear man's coefficient: -.76). Significant differences in creatinine concentrati on were seen among different gestational groups at 24 and 48 hours of life. Peak creatinine correlated with a high Clinical Risk Index for Babies scor e (Spearman's coefficient: .64). The fall in creatinine began later in more premature infants. All 38 surviving infants had normal renal function; the ir mean plasma creatinine at discharge was 52 mmol/L (CI: 46-58 mu mol/L). Conclusions. Rather than falling steadily from birth, creatinine rises dram atically in the first 48 hours of life, especially in infants of <30 weeks' gestation. Even large rises in creatinine in the first 48 hours may be exp ected and should not be used in isolation to diagnose renal failure.