Development of a new immunoassay for the detection of ethyl glucuronide (EtG) in meconium: validation with authentic specimens analyzed using LC-MS/MS. Preliminary results

Background: Ethyl glucuronide (EtG) measurement in neonatal meconium has emerged as a reliable marker to objectively assess prenatal exposure to maternal ethanol complementary to fatty acid ethyl ester (FAEEs) measurement. The detection of EtG in meconium is currently a lengthy, difficult and expensive process using liquid chromatography tandem mass spectrometry (LC-MS/MS) as the analytical procedure. An enzyme-linked immunosorbent assay (ELISA) for the identification of EtG in meconium was developed, validated and applied to authentic meconium specimens from newborns collected in Europe. Methods: The ELISA procedure was calibrated using 0.45, 0.9, 1.35 and 1.8 nmol/g (100, 200 300 and 400 ng/g) standards. Meconium (0.25 g) was mixed thoroughly, with extraction buffer (pH 7.3; 0.5 mL). The tube was capped, sonicated, centrifuged and the supernatant was decanted. An aliquot of the extract (50 mu L) was placed in the well of the microplate followed by enzyme conjugate (150 mu L). The plate was incubated for 1 h, washed with deionized water, dried and substrate (200 mu L) was added. After 30 min incubation, stop solution was added and the plate was read at 450 nm and 650 nm. Samples were also analyzed for EtG and FAEEs by validated LC-MS/MS assays. Results: Using an EtG cut-off of 0.9 nmol/g for both ELISA screening test and confirmatory LC-MS/MS, immunoassay sensitivity was 100%; specificity 78%; positive-predictive value (PPV) 29% and negative-predictive value (NPV) 100%. Conclusions: The assay is proposed as a preliminary screening test for the meconium of newborns suspected of being born to mothers drinking alcohol during pregnancy.