Effects of Blood Collection Tubes on the Quantification of Catecholamines and Their O-Methylated Metabolites by Liquid Chromatography Coupled With Tandem Mass Spectrometry.

Background: Catecholamines (epinephrine; norepinephrine; and dopamine) and their O-methylated metabolites (metanephrine; normetanephrine; and 3-methoxytyramine) are biomarkers for pheochromocytoma and paraganglioma. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was recommended by Endocrine Society for detecting these compounds. The influence of blood collection tubes on the analysis of the six analytes by LC-MS/MS was not thoroughly investigated, which we want to clarify in our study.

Methods: Blood samples of healthy individuals were collected into serum, lithium heparin, and K₂EDTA plasma tubes separately. Samples were subjected to solid phase extraction and then analyzed by LC-MS/MS. The retention behavior and assay performance of the six analytes were assessed for samples from different collection containers. The impacts of potassium and sodium as the counter ions of EDTA on the retention time and matrix effect were also studied.

Results: Compared with O-methylated metabolites, the results for catecholamines were more affected by the collection tubes, especially for norepinephrine, which displayed severely suppressed signal and very low extraction efficiency in K₂EDTA plasma. Changing the counter ion of EDTA from potassium to sodium dramatically changed the retention behavior and matrix effect of norepinephrine.

Conclusions: It is necessary to evaluate blood collection tubes for catecholamines and their O-methylated metabolites analyzed by LC-MS/MS. In addition, attention should also be paid when the anticoagulant counter ion was changed.