Multiple positive results during a neonatal screening program: a retrospective analysis of incidence, clinical implications and outcomes.

AIMS: Neonatal screening programs perform different screening tests on the same blood-spot sample collected on a Guthrie card. We retrospectively investigated the incidence of multiple positive results as well as the outcomes and the physical characteristics of newborns with more than one positive result for phenylketonuria (PKU), congenital hypothyroidism (CH) and congenital adrenal hyperplasia (CAH).

METHODS: Neonatal screening was performed on blood-spot for PKU (phenylalanine concentration by fluorescent ninhydrine method), for CH (simultaneous total thyroxin (tT4) and thyroid-stimulating hormone (TSH) levels by fluoroimmunometric assay); and for CAH (17-hydroxyprogesteron level by fluoroimmunometric assay).

RESULTS: During three years of screening, 39 newborns (37 preterms) showed multiple positive results at screening tests (incidence 1:6387). The most frequent positive results were the combinations of CH and CAH (25/39) and PKU and CH (12/39). At recall, only two newborns were confirmed positive and each for only one disease: one, premature baby, for PKU from the PKU and CH combination; the other, born at term, for CAH from the CH and CAH combination.

CONCLUSIONS: Multiple positive results are a rare observation at neonatal screening for PKU, CH and CAH, more frequently observed in preterm babies. However, multiple positive results must not be overlooked because of true positive results at recall.