Creatinaemia at Birth is Equal to Maternal Creatinaemia at Delivery: Does This Paradigm Still Hold?

Objective: The paradigm that creatinaemia at birth is equal to maternal creatinaemia may also depend upon the quantification technique applied. Paired maternal-neonatal creatinaemia samples in whom Jaffe in both or compensated Jaffe (maternal) and enzymatic quantification (neonate) were applied.

Methods: Extreme low birth weight infants in two time intervals were included when paired maternal-neonatal creatinaemia samples were available. In cohort 1 (2000-2005), creatinaemia (mothers and neonates) was based on Jaffe assay. In cohort 2 (2007-2010), maternal creatinaemia was based on compensated Jaffe. In neonates, an enzymatic technique was applied. Unpaired Mann Whitney U, paired Wilcoxon and Bland-Altman were used.

Results: Based on 80 and 52 paired creatinaemia samples, there was no significant difference between maternal (0.80, 0.41-1.6 mg.dl(-1)) and neonatal creatinaemia (0.78, 0.31-1.46 mg.dl(-1)) in cohort 1 while a significant difference (p < 0.001) between maternal (0.6, 0.29-2.24 mg.dl(-1)) and neonatal creatinaemia (0.67, 0.4-2.2 mg.dl(-1)) was observed for cohort 2. Using Bland-Altman, the fit was perfect for cohort 1 (mean diff -0.02 mg.dl(-1)), but not for cohort 2 (-0.08 mg.dl(-1)).

Conclusions: The quantification method affects the paradigm that creatinaemia at birth is similar to maternal creatinaemia. Maternal and neonatal creatinaemia values depend on the method used. Consequently, method-specific reference values are needed.