Background Serum creatinine (Scr) reflects to a certain extent GFR in neonates, but postnatal observations also depends on the technique used (Jaffe colorimetry or enzymatic quantification) as recently quantified in ELBW neonates (1.2). We aimed to assess the impact of enzymatic versus Jaffe quantification and to describe postnatal Scr trends for both techniques in neonates with higher birth weight (3).

Methods Scr values quantified by Jaffe in 1140 neonates were compared to values obtained by enzymatic quantification in 1023 neonates in one NICU. All Scr values collected in the first 42 days of postnatal life were included and postnatal trends for cohorts < 1kg, 1–2 kg, 2–3 kg and > 3 kg were compared.

Results Postnatal patterns were similar between both techniques, with an initial increase of Scr (highest and last in the smallest neonates) in early postnatal life, and a subsequent decrease, most delayed in the smallest neonates. For all consecutive postnatal observations, Jaffe always resulted in higher Scr compared to the enzymatic technique, but the differences in median values between both techniques (0.1–0.26 mg/dl, equal to 8.8–23 µmol/l), were not a fixed value.

Conclusions When using Scr to estimate renal function in neonates, clinicians should in addition to postnatal changes and other covariates of renal function, also consider the technique applied. There is no fixed conversion factor to correct for differences between both techniques.

1. Allegaert, J Matern Fetal Neonatal Med DOI 10.3109/14767058.2012.657277.

2. Kuppens, J Matern Fetal Neonatal Med DOI 10.3109/14767058.2011.602144.

3. Bueva, Pediatr Res 1994.