Stability of the thromboxane B2 biomarker of low-dose aspirin pharmacodynamics in human whole blood and in long-term stored serum samples

Background: Serum thromboxane B2 (sTXB2) is a validated biomarker of low-dose aspirin pharmacodynamics. In the original method, nonanticoagulated blood samples must be incubated at 37 °C immediately after withdrawal, centrifuged and serum supernatant should be frozen until assayed. Timely completion of all preanalytical steps may affect the feasibility and quality of sTXB2 measurements. The storage duration of frozen serum can also affect sTXB2 stability. Objectives: We assessed the stability of sTXB2 in clotted blood samples stored at 4 °C before further processing and in sera stored at -40 °C for over a decade. Methods: Venous whole blood withdrawn from individuals on chronic low-dose aspirin was dispensed in different tubes and immediately incubated at 37 °C for 1 hour. The reference tube was promptly processed following the original protocol; the remaining tubes were stored at 4 °C for 12 to 72 hours before further processing. Sera stored at a controlled -40 °C temperature for <1 to 15 years were reassayed. Values within the interassay variation limits (±9%) vs baseline were considered acceptable. Results: Baseline sTXB2 values (median, 5.4 ng/mL; IQR, 2.4-13.4 ng/mL; n = 40) were comparable with those in samples at 4 °C up to 48 hours (median, 97% [IQR, 86%-104%] of the reference; n = 26), but at 72 hours, the variability exceeded the interassay variation. Thromboxane B2 levels were stable in frozen sera for up to 10 years (median, 101% [IQR, 87%-108%] of the reference; n = 32) but decreased significantly afterward (median, 87% [IQR, 74%-109%] at 15 years; P = .005; n = 32). Conclusion: Thromboxane B2 is stable in clotted blood samples stored at 4 °C for up to 48 hours before further processing and in serum samples stored at -40 °C over 10 years.