Addition of 3-deazaadenosine to vacutainer tubes stabilizes whole-blood homocysteine for at least 6 hours at ambient temperature.

To the Editor: Increased plasma homocysteine is now well established as a risk factor for cardiac, cerebral, and peripheral vascular disease (1). Despite this, the test is not widely available. This is partly because of practical difficulties in sample collection. The homocys-teine concentration increases in whole blood by up to 10% per hour unless samples are kept on ice and separated within 60 min. The introduction of containers with 3-deazaadenosine (3-dad; DS30 Homocysteine Blood Collection Tubes; Drew Scientific Ltd.), described in a recent report (2) in the Journal, may solve the problem, but they are not in widespread use. Furthermore , we feel that stabilization that requires both special tubes and refrigeration of samples has limited practical value, as transportation (which is unrefrigerated) to the laboratory usually requires 2– 6 h, at least in the UK, making the samples unsuitable for homocysteine analysis. This problem can be overcome by preparing tubes that stabilize homo-cysteine by the simple expedient of injecting 3-dad (3), an inhibitor of S-adenosylhomocysteine hydrolase, into standard Vacutainer Tubes. Samples sent to the laboratory in these tubes can then be separated and the plasma sent to a specialist center for homocysteine analysis. Homocysteine in plasma is stable for several days at room temperature. We injected 40 ␮L (10 mmol/L) of 3-dad (Sigma Chemical Company) into 4.0-mL dipotassium EDTA Va-cutainers (Becton Dickinson Vacu-tainer Systems) with an insulin syringe and fine needle. This procedure does not break the vacuum. Control tubes were prepared with 40 ␮L of saline (150 mmol/L). Blood from 10 healthy volunteers was collected in the modified Vacutainers (two saline and two 3-dad tubes from each volunteer). Saline Vacutainer samples were immediately placed on ice and separated within 60 min or incubated at room temperature for 6 h before separation. 3-dad Vacutainer samples were placed on ice and separated after 6 h or incubated at room temperature for 6 h before separation. Total plasma homocysteine was measured after derivatization with ammonium 7-fluorobenzo-2-oxa-1,3-diazole-4-sulfonate (SBDF) and separation of thiols by isocratic reversed-phase HPLC (4). Plasma homocysteine concentrations in samples collected into saline and left to stand at room temperature for 6 h showed a mean (SD) increase of 3.2 (0.9) ␮mol/L compared with samples separated immediately (P Ͻ0.01, Mann–Whitney). In contrast, samples collected into 3-dad showed no increase in plasma homocysteine concentration over 6 h whether the samples were left at room temperature [Ϫ0.4 (0.3) ␮mol/L; P ϭ 0.76] …