Microassay for screening newborns for galactosemia with use of a fluorometric microplate reader

We describe a microassay for measuring galactose (Gal) and galactose 1-phosphate (Gal-1-P) in dried blood spots. After a coupled enzyme reaction involving galactose dehydrogenase (GADH, EC 1.1.1.48) and alkaline phosphatase (AP, EC 3.1.3.1) in a microplate well, NADH fluorescence is measured by a highly sensitive fluorometric microplate reader, capable of rapid measurement of fluorescence (2 min per 96 samples). Within- and between-run CVs for measurements of Gal at 90 mg/L with Gal-1-P at 130 mg/L were both less than 5% (n = 8), and analytical recoveries for Gal at 90 mg/L and Gal-1-P at 130 mg/L were 98% and 92%, respectively. Five hundred dried blood-spot samples can be assayed within 2 h, with full calculation of results by an on-line microcomputer. This rapid and reliable assay system is very useful for the routine screening of newborns for galactosemia.