Age-Related Variations in Acylcarnitine and Free Carnitine Concentrations Measured by Tandem Mass Spectrometry (Laboratory Management‪)‬

Analysis of the free Carnitine (FC) (4) and acylcarnitine (AC) profiles by tandem mass spectrometry (MS/MS) has improved the detection of inherited errors of metabolism (IEM) in newborns (1). This method allows the screening, through a single test using very small dried blood samples, of several IEM of amino acids, organic acidurias, and fatty acid oxidation disorders (2, 3). Moreover, this technique has been demonstrated to be highly sensitive and specific (4, 5). In some laboratories, screening by MS/MS has nearly doubled the rates of detection of metabolic disorders compared with conventional methods (6). Reference values for FC and AC profiles by MS/MS have been calculated from the whole-blood concentrations measured in healthy newborns, a period of intense fatty acid metabolism (7,8). Because the concentration of metabolites such as amino acids and organic acids can change markedly with age, variations in FC and AC concentrations could have a potential impact on the accuracy of the diagnosis and optimal management of patients with IEM. In this study, we measured FC and AC concentrations by MS/MS in dried blood samples obtained from birth to adulthood.