Biological Variation of Free and Total Carnitine in Serum of Healthy Subjects

Abstract

Determination of carnitine (l-β-hydroxy-γ-trimethylaminobutyric acid) in biological samples plays an important role in the diagnosis of diseases with carnitine deficiency (1). In the past few years, and also in this Journal, several spectrophotometric methods for assaying carnitine in serum have been described (2)(3)(4)(5)(6). To our knowledge, however, no data have been published on the biological variation of this serum analyte. For any new test, data on the biological variation generated from the healthy population may be used (a) in setting desirable performance standards or analytical goals, (b) in assessing the utility of conventional population-based reference intervals, and (c) in critically evaluating the significance of changes in serial results from an individual (7). To investigate the analytical and biological variation of free and total carnitine, as well as of the acyl/free carnitine ratio, we collected blood samples once a week for 4 weeks from each of 14 healthy subjects (7 men and 7 nonpregnant women, ages 21–23 years), students of Mathias Belius University. The subjects agreed to maintain current dietary habits, body weight, and exercise program (if any) for the duration of the study. The criteria of the hospital Ethics Committee were respected in this experiment. To minimize sources of preanalytical variation, venous blood specimens were drawn between 0800 and 0900 h after ∼12 h of fasting. The subjects …