Addition of Sodium Fluoride to Whole Blood Does Not Stabilize Plasma Homocysteine But Produces Dilution Effects on Plasma Constituents and Hematocrit

摘要

Interest in total plasma homocysteine (Hcy) measurements has increased with the availability of evidence that even mild hyperhomocysteinemia is an independent risk factor for cardiovascular disease (1). Consequently, the variability of current Hcy results has been the subject of considerable research (2)(3)(4). Whole blood stored at room temperature after phlebotomy shows an increase in Hcy concentrations of ～10% per hour, apparently because of Hcy synthesis and release from erythrocytes (5)(6). Previous studies have shown that the best method for avoiding falsely high Hcy results is prompt postphlebotomy centrifugation and separation of the plasma from the red blood cells (6) or storage of whole blood samples at 0 °C if prompt centrifugation is not feasible (3). The use of anticoagulants as preservatives in whole blood has also been advocated (2)(3)(4); among these, sodium fluoride (NaF) in particular has been described as useful when added to whole blood at suggested concentrations of up to 4 g/L (95 mmol/L) (4)(7).Many laboratories, therefore, now use NaF as a preservative in the blood collection tubes used for Hcy assays. We measured plasma Hcy, using a modified version of the HPLC method with fluorescence detection introduced by Refsum and co-workers (8), after the addition of pure NaF (2.5 g/L, 60 mmol/L) to heparinized whole blood. The studies were approved by the University of Washington Institutional Review Board and involved the donation of blood from men and women after informed consent. We found minimal inhibition of the time-dependent increase in Hcy concentrations. We also investigated the preservative abilities of Na2EDTA (1.5 g/L, 4.0 mmol/L), EGTA (1.5 g/L, 3.9 mmol/L), and thymol (1.0 g/L, 6.6 mmol/L), again added in pure form to heparinized whole …