You have an 11-day-old term infant in your office for a well-child visit. The mother notes that she received a letter that day from the state's Department of Health reporting that her child's newborn screen had come back abnormal, indicating possible galactosemia. Which of the following is the most appropriate management at this point?
a) Initiate a galactose-free diet
b) Repeat the newborn screen
c) Obtain a galactose-1-phosphate uridyltransferase (GALT) enzyme assay
d) Start lactose-free formula supplementation