Background: Parenteral nutrition (PN) is a nutrient solution administered intravenously (IV) to premature babies. PN causes elevations of some amino acids in blood samples that are also biomarkers used in newborn screening (NBS). Therefore, PN status must be annotated on dried blood spot (DBS) cards by clinicians to reduce NBS laboratory burdens associated with potential false results, however, NBS laboratories continue to receive DBS with misannotated PN status. N-acetyltyrosine (NAT), a water-soluble tyrosine analog used to increase tyrosine bioavailability in PN solutions, can be used as a blood-based biomarker of PN administration in NBS assays.
Methods: Residual DBS specimens and manufactured DBS were used in analyses. The assay was developed and validated using flow injection analysis tandem mass spectrometry (FIA-MS/MS) for detection of NAT.
Results: NAT was only present in neonate DBS with annotated PN administration, and was multiplexed into first-tier newborn screening assays. NAT was highly correlated with amino acids present in PN solutions such as arginine, leucine, methionine, phenylalanine, and valine. In our sample cohort, we determined an NAT cutoff could aid identification of misannotated neonates administered PN. We also report the Amadori rearrangement product valine-hexose (Val-Hex) was quantifiable in neonates administered PN, which we suspect forms in the PN solution and/or IV lines.
Conclusions: Here we present the first known use of NAT as a biomarker for PN administration, which is currently being piloted by two U.S. NBS laboratories. NAT and Val-Hex can aid identification of misannotated DBS from neonates administered PN, thus, decreasing false positive rates.
