Impact of second-tier testing on the effectiveness of newborn screening

In one study, MS/MS analysis of newborn spot samples of dried blood collected ≤24 h after birth was compared with fluorometric analysis of the same samples. Because of this early time of collection, the decision level for an increased phenylalanine concentration was lowered by the public health laboratory using fluorometry to ensure that no infants with phenylketonuria were missed. [...] the primary screening of congenital adrenal hyperplasia is done with less selective methods, with a larger capture of presumptive positive cases being followed by a second-tier analysis.