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 B 2 (sTXB 2 ) 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 sTXB 2 measurements. The storage duration of frozen serum can also affect sTXB 2 stability. Objectives We assessed the stability of sTXB 2 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 Methods Venous whole blood withdrawn from individuals on chronic low-dose aspirin was dispensed in different tubes and immediately incubated at 37 °C for 1 hour.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 sTXB 2 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 B 2 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 B 2 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.