Comparison of the effects of season and prematurity on the enzymatic newborn screening tests for galactosemia and biotinidase deficiency

In the Commonwealth of Virginia, 299,420 newborns were screened for biotinidase deficiency and galactosemia during the years 1989-1991 using enzymatic assays for galactose-l-phosphate uridyl transferase activity and biotinidase activity on dried blood filter paper cards. Retrospectively, false-positive initial samples for galactosemia or biotinidase deficiency were identified, and monthly frequencies of false-positive results were determined. The false-positive rates for galactosemia and biotinidase deficiency screening decreased over the 3-year period and were significantly higher in galactosemia screening for each year examined P < 0.001). For galactosemia screening, monthly false-positive rates were highest during May through September, seasonal differences in false-positive rates were significant for each year evaluated (P < 0.001). and seasonal false-positive rates for the 3 years combined were highest during the summer and lowest during the winter. For biotinidase deficiency, differences in seasonal false-positive rates were significant in 1989 (P<0.001) and 1991 (P<0.01), and the highest seasonal false-positive rate for the 3 years combined occurred in the spring. Average monthly temperature and year of measurement were significant factors in galactosemia screening only (P< 0.0001) and accounted for much of the variance in false-positive rates (r² = 0.43). Approximately half of the infants with false-positive results for biotinidase deficiency were premature, significantly more than the incidence of prematurity in Virginia (7-8%) during the 3 years (P<0.001). Prematurity in false-positive galactosemia screens was not significantly different from expected rates.