Stability of plasma total homocysteine concentrations in EDTA-whole blood kept on ice.

In recent years there has been increasing interest in monitoring plasma total homocysteine concentration (tHcy), as a risk factor for thrombotic disorders. One of the significant preanalytical factors that can affect the reliability of tHcy measurements is the generation of homocysteine by erythrocytes in vitro, prior to the separation of plasma from cells. We measured changes in tHcy from EDTA-whole blood kept on ice and at room temperature for three hours. Compared to the tHcy in plasma from EDTA-whole blood that was processed immediately after collection, there was no significant change in tHcy in samples kept on ice for up to three hours prior to processing (mean change = -0.1 +/- 0.24 umol/L, p = 0.2). In contrast, tHcy in samples kept at room temperature increased by 0.7 +/- 0.2 mumol/L per hour, p < 0.001. We conclude that tHcy is stable in EDTA-whole blood for at lest three hours, provided that the tubes are kept on ice until they are processed.