Objective To investigate the feasibility of analyzing acylcarnitine in dry filter-paper blood spots by liquid chromatography-tandem mass spectrometry (LC-MS/MS) which could be applied to detect inborn errors of metabolism in neonates. Methods We obtained filter-paper blood from 26 dead infants from a neonatal intensive care unit (NICU) between October 1

2008 and September 30

2009. Acylcarnitine and amino acid profiles were obtained with LC-MS/MS. Four infants underwent routine autopsy. The postmortem blood specimens were compared with newborn blood specimens

and with specimens obtained from older infants with metabolic disorders. Results Of all the 26 patients

5 (19.2%) were diagnosed as having different kinds of diseases: 3 with methylmalonic acidemia (the concentration of C3

and the ratio of C3/C16

C3/C2 increased)

1 with maple syrup urine disease (the concentration of leucine and isoleucine increased)

and 1 with isovaleric aci- demia (the concentration of C5 increased). Conclusions Postmortem metabolic test can explain infant deaths and provide estimates of deaths attributable to inborn errors of metabolism in NICU. LC-MS/MS is suitable for analysis of postmortem specimens and can be considered for routine application in NICU autopsy.