Increased C3-carnitine in a healthy premature infant.

A 5-day-old male infant with an increased dried blood spot propionylcarnitine (C3-carnitine) value of 7.93 mol/L (cutoff 6.79 mol/L) was identified by the New Jersey state newborn screening program. C3carnitine 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. On day of life 6, the patient developed a mild acidosis (pH 7.24 on arterial blood gas testing). Because methylmalonic and propionic acidemia could not be excluded while confirmatory test results were pending, feedings were discontinued, intravenous hydration with glucose-containing fluids was initiated, and the infant was transferred to our institution. On arrival the child appeared well, was alert, and had normal growth parameters and no tachypnea. He had good tone and normal reflexes, and laboratory studies showed no acidosis. We allowed normal feedings and proceeded with the diagnostic evaluation.