BACKGROUND: Myeloperoxidase (MPO) has shown potential as a marker for cardiovascular disease. Limited studies have been published with a variety of sample types, resulting in a wide range of MPO values. Little is known or understood about the impact of collection tube type and preanalytical handling of specimens for MPO determination.

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Background: Choline is critical for a variety of biological functions and has been investigated as a biomarker for various pathological conditions including acute coronary syndrome. Methods: A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was used to quantify choline in whole blood and plasma in freshly collected samples prepared with ultrafiltration or protein precipitation. We investigated the effects of preanalytical variables including types of anticoagulants and storage temperature and time. Results: We observed no significant differences in whole-blood choline concentration in EDTA-anticoagulated vs heparin-anticoagulated samples: mean (SD) difference 0.9% (3.2%), P = 0.80. For plasma, choline concentrations with heparin in 5 of 12 volunteers were >10% higher than with EDTA, P = 0.01. One freeze-thaw cycle led to significant mean (SD) increases in choline concentrations in heparin whole blood, 19.3% (11.4%), P <0.01, and the effect was not significant for other sample types studied (P >0.33). For freshly collected samples stored at ambient temperature, choline concentrations in all types of samples increased with storage time. For EDTA whole blood, EDTA plasma, and heparin plasma, the choline concentration increased for the first 60 min and then stabilized. For heparin whole blood, the choline concentration continued to increase linearly with storage time for >4 h, at which time the choline concentrations were increased by approximately 50%. Conclusions: Sample collection, storage, and sample preparation procedures are critical for clinical measurements of choline in whole blood and plasma.