Stability of the thromboxane B2 biomarker of 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, non-anticoagulated blood samples must incubate at 37°C immediately after withdrawal, be centrifuged, serum 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.Aims. We assessed the stability of sTXB2: in clotted blood samples stored at 4°C before further processing; in sera stored at -40°C for over a decade.Method. Venous whole blood withdrawn from individuals on chronic low-dose aspirin was dispensed in different tubes, immediately incubated at 37°C for 1 hour.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 from 12 to 72 hours before further processing. Sera stored at controlled -40°C temperature for <1 to 15 years were re-assayed. Values within the inter-assay variation limits (±9%) versus baseline were considered acceptable. Results. Baseline sTXB2 values (5.4[2.4-13.4] ng/ml, median [IQR], n=40) were comparable with those in samples at 4°C up to 48 hours (97[86-104]% of reference, n=26), but at 72 hours the variability exceeded the inter-assay variation. TXB2 levels were stable in frozen sera for up to 10 years (101[87-108]% of reference, n=32), but decreased significantly afterwards (87[74-109]% at 15 years, p=0.005, n=32).Conclusions. TXB2 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.