In most regions, galactosemia is diagnosed as a result of newborn screening, most commonly by determining the concentration of galactose in a dried blood spot. Some regions will perform a second-tier test of GALT enzyme activity on samples with elevated galactose, while others perform both GALT and galactose measurements. While awaiting confirmatory testing for classic galactosemia, the infant is typically fed a soy-based formula, as human and cow milk contains galactose as a component of lactose. Confirmatory testing would include measurement of enzyme activity in red blood cells, determination of Gal-1-P levels in the blood, and mutation testing. The differential diagnosis for elevated galactose concentrations in blood on a newborn screening result can include other disorders of galactose metabolism, including galactokinase deficiency and galactose epimerase deficiency. Enzyme assays are commonly done using fluorometric detection or older radioactively labeled substrates.
Galactose-1-phosphate uridylyltransferase deficiency
Arginine:glycine amidinotransferase deficiency
Ribose-5-phosphate isomerase deficiency
Malonyl-CoA decarboxylase deficiency
Ornithine aminotransferase deficiency
Galactose epimerase deficiency
Guanidinoacetate methyltransferase deficiency
Adenine phosphoribosyltransferase deficiency