Tamara van Donge

Chapter 7 140 0.20 0.25 0.30 0.35 0.40 1 3 5 7 9 11 13 15 Time after birth (days) Creatinine clearance (ml/min) Figure 4: Simulated creatinine clearance of a typical patient of 27 weeks gestational age delivered by C-section receiving seven days of ibuprofen treatment, starting on third day after birth (red) or without receiving ibuprofen treatment (blue). Interestingly, a high ratio >1 (indicating higher amount of creatinine produced than eliminated) was observed during the first three days despite constant production of creatinine and increase in clearance of creatinine after birth. It may be hypothesized that this observation is linked to reabsorption of creatinine by immature renal tubules and that both postnatal (time after birth) and prenatal (gestational age) maturation reduce the reabsorption capability of these tubules. Findings (or results) in our study indicate that GA is an additional factor associated to this ratio, meaning that the amount of creatinine that is being reabsorbed differs per GA. Finally, especially in a population where the blood volume available for sampling is limited and the risk of anemia is high, restrained management should be pursued when collecting blood samples for e.g. Scr determination. The developed reference ranges could help gain insights in normative creatinine profiles in ELBW neonates and assist on the discrimination between whether a change in Scr concentration is either due to developmental physiological