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 period are higher in more premature infants. However, the best reference data commence on day 2 of life. The objective of this study was to document how plasma creatinine changes in the first 48 hours of life and to examine the reason for the apparently high levels of creatinine in preterm infants, compared 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 gestation groups: 23 to 26 weeks (n = 9), 27 to 29 weeks (n = 13), 30 to 32 weeks (n = 12), and 33 to 35 weeks (n = 8). Interventions. Measurement of plasma creatinine and urea concentration in cord blood and in serial samples taken for routine arterial blood gas analysis. Outcome Measurements. Changes in creatinine concentration with time and relationship 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 related to gestation (Spearman's coefficient: 2. 73) and birth weight (Spearman's coefficient: -.76). Significant differences in creatinine concentration were seen among different gestational groups at 24 and 48 hours of life. Peak creatinine correlated with a high Clinical Risk Index for Babies score (Spearman's coefficient: .64). The fall in creatinine began later in more premature infants. All 38 surviving infants had normal renal function; their mean plasma creatinine at discharge was 52 mmol/L (CI: 46-58 mu mol/L). Conclusions. Rather than falling steadily from birth, creatinine rises dramatically 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 expected and should not be used in isolation to diagnose renal failure.