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Surprising causes of C5-carnitine false positive results in newborn screening

François Boemer1, Roland Schoos1, Virginie de Halleux2

  • 1Biochemical Genetics Laboratory, Human Genetics, CHU Liege, University of Liege, Belgium.

Molecular Genetics and Metabolism
|December 3, 2013
PubMed

Insights

A nipple cream containing neopentanoate-esters caused false positives in newborn screening for isovaleric acidemia. Removing this product from distribution significantly reduced false positive rates, improving screening accuracy.

Area of Science:

  • Biochemistry
  • Neonatal Screening
  • Toxicology

Background:

  • Newborn screening programs aim to detect metabolic disorders early.
  • An unexplained rise in false positives for isovaleric acidemia was observed.
  • Elevated C5-carnitine levels are an indicator for isovaleric acidemia.

Purpose of the Study:

  • To investigate the cause of increased false positivity in newborn screening for isovaleric acidemia.
  • To identify the source of pivaloylcarnitine detected in newborns.

Main Methods:

  • Analysis of newborn blood samples for C5-carnitine and pivaloylcarnitine.
  • Investigating the source of exogenous pivalate exposure.
  • Monitoring screening positivity rates after product withdrawal.

Main Results:

  • All 50 newborns with elevated C5-carnitine showed detectable pivaloylcarnitine.
  • Neopentanoate-esters, a derivative of pivalic acid, were identified in a nipple-fissure unguent.
  • Discontinuation of the unguent led to a substantial decrease in false positive screening results.

Conclusions:

  • Topical neopentanoate-ester exposure from unguents can cause false positives in newborn screening for isovaleric acidemia.
  • Environmental and iatrogenic factors must be considered in newborn screening.
  • Product reformulation or withdrawal is crucial to maintain screening specificity.

Keywords:
C5-carnitineFalse positiveInborn error of metabolismMass spectrometryNewborn screeningPivalic acid

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