DOI: 10.1373/clinchem.2008.107581


A 5-day-old male infant with an increased dried blood spot propionylcarnitine (C3-carnitine) value of 7.93 μmol/L (cutoff <6.79 μmol/L) was identified by the New Jersey state newborn screening program. C3-carnitine is used as a screening tool for methylmalonic and propionic acidemias, potentially fatal but treatable inborn errors of metabolism. The initial screen values provided a calculated C3:C2 carnitine ratio of 0.23 (cutoff <0.32, mean 0.074) and a C3:C16 ratio of 2.51 (cutoff <4.16, mean 0.96). The child was an inpatient at an outlying neonatal intensive care unit. He was born at 35 weeks estimated gestational age, required continuous positive airway pressure for a short time after birth, and transitioned quickly to room air. He was taking regular feedings with a cow’s milk protein–based formula.