Carnitine transporter defect diagnosed by newborn screening with electrospray tandem mass spectrometry

The carnitine transporter defect is a potentially fatal but treatable disor der. We used electrospray tandem mass spectrometry in the New South Wales ( Australia) Newborn Screening Programme to measure free carnitine and acylca rnitine species in the newborn population, Free carnitine levels in dried b lood samples from 149,000 neonates did not vary markedly between 2 and 8 da ys of age. Two of 4 babies subsequently diagnosed clinically with the carni tine transporter defect had a free carnitine level in the neonatal blood sa mple low enough to be detected by screening.