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 (20002005), creatinaemia (mothers and neonates) was based on Jaffe assay. In cohort 2 (20072010), 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, 0.411.6mg.dl^-1) and neonatal creatinaemia (0.78, 0.311.46mg.dl ^-1) in cohort 1 while a significant difference (p<0.001) between maternal (0.6, 0.292.24mg.dl^-1) and neonatal creatinaemia (0.67, 0.42.2mg.dl^-1) was observed for cohort 2. Using Bland-Altman, the fit was perfect for cohort 1 (mean diff -0.02mg.dl^-1), but not for cohort 2 (-0.08mg.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.