OBJECTIVE: Tandem mass spectrometry is widely applied to routine newborn screening but there are no long-term studies of outcome. We studied the clinical outcome at six years of age in Australia.

METHODS: In a cohort study, we analyzed the outcome at 6 years for patients detected by screening or by clinical diagnosis among >2 million infants born from 1994 to 1998 (1 017 800, all unscreened) and 1998 to 2002 (461 500 screened, 533 400 unscreened) recording intellectual and physical condition, school placement, other medical problems, growth, treatment, diet, and hospital admissions. Results were analyzed separately for medium-chain acyl-CoA dehydrogenase deficiency (MCADD) and other disorders, and grouped patients as those who presented clinically or died in the first 5 days of life; patients presented later or diagnosed by screening, and those with substantially benign disorders.

RESULTS: Inborn errors, excluding phenylketonuria, were diagnosed in 116 of 1 551 200 unscreened infants (7.5/100 000 births) and 70 of 461 500 screened infants (15.2/100 000 births). Excluding MCADD, 21 unscreened patients with metabolic disorders diagnosed after 5 days of life died or had a significant intellectual or physical handicap (1.35/100 000 population) compared with 2 of the screened cohort (0.43/100 000; odds ratio: 3.1 [95% CI: 0.73–13.32]). Considering the likely morbidity or mortality among the expected number of never-diagnosed unscreened patients, there would be a significant difference. Growth distribution was normal in all cohorts.

CONCLUSION: Screening by tandem mass spectrometry provides a better outcome for patients at 6 years of age, with fewer deaths and fewer clinically significant disabilities.

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