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Clinica chimica acta; international journal of clinical chemistry

Stable-isotope dilution measurement of isovalerylglycine by tandem mass spectrometry in newborn screening for isovaleric acidemia.


PMID 17850781

Abstract

Recent neonatal screening for isovaleric acidemia by tandem mass spectrometry based on dried blood-spot levels of C5-acylcarnitines, including isovalerylcarnitine and its isomer, pivaloylcarnitine, which is derived from pivalate-generating antibiotics, has caused many false-positive results. We have developed a method to overcome this interference. The amounts of isovalerylglycine were determined by a stable-isotope dilution electrospray tandem mass spectrometric analysis, using multiple-reaction monitoring with product ions of m/z 132, which were generated predominantly from quasi-molecular ions of isovalerylglycine butylester but apparently not from those of pivaloylglycine butylester. Isovalerylglycine concentrations in dried blood spots of control newborns were 0.17+/-0.03 nmol/ml, and those of patients with isovaleric acidemia ranged from 1.3 to 80.0 nmol/ml. Those of the newborns treated with antibiotics, which caused high C5-acylcarnitine levels (1.9+/-1.7 nmol/ml) in dried blood spots, were 0.22+/-0.05 nmol/ml. Our data showed that the present method is useful in eliminating the false-positive results due to antibiotics use in newborn screening for isovaleric acidemia.

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43424
N-Isovalerylglycine, ≥97.0% (GC)
C7H13NO3