Disorders of vitamin B12 metabolism presenting through newborn screening.

Elevated propionyl C3 carnitine is the most common abnormality seen in tandem mass spectrometry newborn screening profiles, with an incidence of 0.15% seen in our South Australian newborn screening programme. The most common cause for this result in our population is vitamin B12 deficiency but differential diagnoses include the inherited disorders of propionic and methylmalonic acid metabolism and cobalamin deficiencies. An approach to confirmatory testing and subsequent management of infants with elevated propionic carnitine is presented.