Creatinaemia at birth is equal to maternal creatinaemia at delivery: does this paradigm still hold?

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.

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.

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)).

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.