Automated fluorometric analysis of galactose in blood

In galactosemia, prevention of mental retardation depends on early recognition of the disorder and institution of dietary restriction of galactose. We describe an automated fluorometric micromethod for galactose in whole blood spotted on filter paper. Galactose is oxidized by galactose oxidase to D-galacto-hexadialdose and H2O2 and measured as the highly fluorescent condensation product of homovanillic acid formed when H2O2 is acted upon by horseradish peroxidase. The procedure is 10-fold more sensitive than colorimetric procedures for galactose and is not hampered by the nonspecific fluorescence from endogenous NADPH that is encountered in methods in which galactose dehydrogenase is used. At a sampling rate of 40/h with a sample-to-wash ratio of 1/2, carryover is negligible, reproducibility is excellent, and 80% of steady state is achieved. Analytical recovery of added galactose was 95%. The method has the requisite sensitivity and accuracy for quantification of galactosemia and galactosuria in milkfed newborn infants and genetic evaluation of families of patients.