A Significant Difference in the Blood Carnitine Values Obtained by the Enzymatic Cycling and Tandem Mass Spectrometry Methods.

BACKGROUND: There are no reports in the literature of blood samples obtained from the same individual being subjected to analysis at the same time using the enzymatic cycling (EC) method along with electrospray tandem mass spectrometry (ESI/MS/MS) before and after carnitine treatment.

METHODS: Blood samples from 29 patients (median age: 73 years old, age range: 41 - 89 years) receiving regular hemodialysis for chronic renal failure before and after carnitine treatment for 3 months were measured by the EC method, and using a dried blood spot (DBS) and ESI/MS/MS.

RESULTS: Before the carnitine treatment, the rate of increase or decrease in the free and acyl-carnitine levels of the DBS using the ESI/MS/MS method to those measured by the EC methods was a median of -28.6% (-36.0 to -14.1%) and -20.8% (-30.0 to 1.5%), respectively. After carnitine treatment, the rate of increase or decrease in the free and acyl-carnitine levels of the DBS with the ESI/MS/MS method compared to the EC method was a median of 52.0% (28.4 to 66.7%) and -31.9% (-47.2 to -21.1%), respectively.

CONCLUSIONS: There were significant differences in the blood carnitine values using the ESI/MS/MS and EC methods. Caution should be exercised when evaluating DBS values measured by the ESI/MS/MS method.