Stability of thromboxane in blood samples.

Conventional venous blood collection requires a puncture with a needle through the endothelium of a vessel. The endothelial injury causes activation of circulating platelets and the release of thromboxane A. The aim of the study was to investigate if platelets continue to form thromboxane A in the blood tube after sample collection, but such synthesis would give false information about the actual circulating thromboxane A value. Thromboxane B is a biologically inactive but stable metabolite of thromboxane A and can be measured in blood samples by a standard enzyme immunoassay. Thromboxane B measurements reflect thromboxane A concentration. Blood samples were collected in 3.2% sodium citrate vials and EDTA vials from ten individuals and centrifuged and frozen at different time points (0, 30, and 120 minutes). Plasma aliquots were transferred to and frozen in 1.8 mL polypropylene tubes and the citrate samples were also transferred to and frozen in propylene tubes containing indomethacin. Concentrations of thromboxane B in plasma samples collected in citrate vials and stored in propylene tubes increased very rapidly as the samples were left for longer after sampling and allowed to stand at room temperature. After 120 minutes, the amount of thromboxane B was 400% higher than in the reference sample at time zero. In comparison, thromboxane B concentration was about 200% higher in the 120-minute samples compared to the reference in samples collected in citrate vials but stored in indomethacin tubes. In samples collected in EDTA vials, a 10% reduction in thromboxane B concentration in the 120-minute samples was observed. Storage conditions, type of sampling vial and time from sampling until sample processing (centrifuging) has a major impact on thromboxane B stability.