Tamara van Donge

Dynamics of creatinine in ELBW neonates 139 7 27 weeks GA 32 weeks GA Wt (g) Scr (mg/dl) CrCL (ml/min) Wt (g) Scr (mg/dl) CrCL (ml/min) 779 0.61 [0.38 - 0.98] 0.23 [0.14 - 0.39] 889 0.79 [0.50 - 1.29] 0.24 [0.14 -0.41] 778 0.87 [0.57 - 1.19] 0.27 [0.16 - 0.45] 887 0.86 [0.56 - 1.24] 0.31 [0.17 -0.49] 790 0.72 [0.45 - 1.30] 0.37 [0.19 - 0.57] 907 0.61 [0.39 - 1.17] 0.43 [0.23 -0.65] 854 0.51 [0.35 - 0.97] 0.48 [0.27 - 0.71] 1000 0.44 [0.31 - 0.73] 0.56 [0.35 -0.78] 935 0.44 [0.31 - 0.71] 0.56 [0.35 - 0.78] 1168 0.39 [0.29 - 0.55] 0.63 [0.44 -0.84] 1053 0.40 [0.29 - 0.59] 0.61 [0.42 - 0.83] 1322 0.36 [0.28 - 0.50] 0.67 [0.49 -0.86] 1205 0.38 [0.29 - 0.52] 0.64 [0.46 - 0.85] 1434 0.35 [0.28 - 0.47] 0.69 [0.52 -0.87] 1387 0.36 [0.28 - 0.50] 0.67 [0.49 - 0.86] 1513 0.34 [0.28 - 0.45] 0.71 [0.55 -0.88] Sixth, our study showed that increasing GA is associated with a steeper increase in GFR over the postnatal period (shorter t 50 ). No inter-individual variability could be estimated on kin production , as it was assumed that the production rate of creatinine remained constant for our ELBW population due to the fact that creatinine is a product which is generated exclusively from muscle metabolism. Previous studies have shown that the fraction of muscle mass does not differ substantially across gestational ages within ELBW cases 26,27 , suggesting that a weight-normalized kin production could have been appropriate. Our estimate of 3.55 mg/day for an average 0.7 L/kg ELBW neonate corresponds to a weight-normalized production rate of 5.1 mg/kg/day, which is approximately half of adult values, and can be considered consistent since factional muscle mass is approximately half that of adults. Additionally, immature renal tubules in ELBW neonates have poor concentrating ability. 28 As such, these immature and leaky renal tubules are partially responsible for passive tubular reabsorption of the filtered and accumulated Scr, mostly during the first postnatal days (Figure S3). 10,29 The ratio of the amount of creatinine produced versus eliminated over time conceptually illustrates that not acute postnatal kidney function decrease but simply low clearance relative to creatinine production, is responsible for the initial rise in Scr after birth. Postnatal water volume constriction might be another contributing factor to this transient increase in Scr, although repeated weight measurements in the first days of life in ELBW cases are uncommon in clinical practice.