Proposed Plasma Ammonia Reference Intervals in a Reference Group of Hospitalized Term and Preterm Neonates

Theresa Madigan, Darci R. Block, William A. Carey, Bethany D. Kaemingk, Robin Patel

Research output: Contribution to journalArticlepeer-review

Abstract

BACKGROUND: Plasma ammonia is commonly measured in the diagnostic evaluation of hospitalized newborns, but reference values are not well defined. METHODS: We prospectively enrolled newborns admitted to the level III/IV neonatal intensive care unit and level II intermediate special care nursery from January 2017 to January 2018. Infants with inborn errors of metabolism or liver disease were excluded. Plasma ammonia concentrations were measured once within the first week of life and evaluated by sex, gestational age, timing of the draw, blood collection method, and type of nutrition. Reference intervals were calculated. RESULTS: 127 neonates were included; one third (34%) were term infants born at ≥37 weeks gestation, and two thirds (66%) were born preterm at <37 weeks gestation. Median plasma ammonia concentrations were 32 μmol/L (range <10 to 86 μmol/L). Median ammonia concentrations were higher among preterm compared to term infants (35 vs. 28 μmol/L, p = 0.0119), and term female compared to term male infants (34 vs. 26 μmol/L, p = 0.0228). There was no difference in median ammonia concentrations between female and male preterm infants, based on gestational age within the preterm group, timing of the blood draw, presence of hyperbilirubinemia, blood collection method, or type of nutritional intake. CONCLUSIONS: Plasma ammonia concentrations among newborns are higher than the expected adult concentrations and may vary by gestational age and sex. Blood collection method, type of nutrition, hyperbilirubinemia, and timing of the draw do not impact concentrations. We propose a reference limit of ≤82 μmol/L for newborns less than one week of age.

Original languageEnglish (US)
Pages (from-to)363-369
Number of pages7
JournalThe journal of applied laboratory medicine
Volume5
Issue number2
DOIs
StatePublished - Mar 1 2020

Keywords

  • Ammonia
  • inborn error of metabolism
  • newborn

ASJC Scopus subject areas

  • Medicine(all)

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