ESI-MS/MS measurement of free carnitine and its precursor γ-butyrobetaine in plasma and dried blood spots from patients with organic acidurias and fatty acid oxidation disorders

Parallel measurements in plasma and DBS demonstrated that numerous patients with low values in DBS had normal values when measured in plasma, suggesting plasma to be the more appropriate medium to use for carnitine status monitoring. In contrast, diagnosis of CPT-I deficiency may be missed when analysis is performed in plasma. Carnitine supplementation presumably inhibits γ-butyrobetaine dioxygenase and results in high γ-butyrobetaine.