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

Mol Genet Metab. 2014 Jan;111(1):52-4. doi: 10.1016/j.ymgme.2013.11.005. Epub 2013 Nov 19.


During an 18-month period, we noticed an alarming increase of newborn screening false positivity rate in identifying isovaleric acidemia. In 50 of 50 newborns presenting elevated C5-carnitine, we confirmed the presence of pivaloylcarnitine. Exogenous pivalate administration had been previously identified as the causal agent of this concern. No pivalic-ester prodrug is commercially available in Belgium, but pivalic derivates are also used in the cosmetic industry as emollient under the term "neopentanoate". We have identified neopentanoate-esters in a nipple-fissure unguent that was provided to young mothers. Ceasing distribution of this product hugely reduced the C5-carnitine false positivity rate.

Keywords: C5-carnitine; False positive; Inborn error of metabolism; Mass spectrometry; Newborn screening; Pivalic acid.

MeSH terms

  • Amino Acid Metabolism, Inborn Errors / diagnosis*
  • Amino Acid Metabolism, Inborn Errors / metabolism
  • Belgium
  • Carnitine / analogs & derivatives
  • Carnitine / blood*
  • False Positive Reactions
  • Humans
  • Infant, Newborn
  • Isovaleryl-CoA Dehydrogenase / deficiency*
  • Isovaleryl-CoA Dehydrogenase / metabolism
  • Mass Spectrometry
  • Neonatal Screening*
  • Ointments
  • Pentanoic Acids / administration & dosage
  • Prodrugs / pharmacology*
  • Risk Factors


  • Ointments
  • Pentanoic Acids
  • Prodrugs
  • pivalic acid
  • pivaloylcarnitine
  • Isovaleryl-CoA Dehydrogenase
  • Carnitine

Supplementary concepts

  • Acidemia, isovaleric