Stability of urinary thromboxane A2 metabolites and adaptation of the extraction method to small urine volume

Background: Thromboxane (TX) A2 is a pro-thrombotic prostanoid synthesized by activated platelets, biotransformedinto 11-dehydro-TXB2, measurable in urines. Eleven-dehydro-TXB2 excretion is increased in high riskcardiovascular diseases; however, this cardiovascular biomarker awaits validation in large trials. The need oflarge urine volume (8 - 10 mL) and the unknown stability of 11-dehydro-TXB2 in urine after collection might limitits implementation.Methods: We scaled the original method for urine extraction and 11-dehydro-TXB2 measurement down to 1 mL,and assessed its stability at 4°C or 25°C up to 6 days after collection. The sensitivity of the 1 mL procedure was alsotested in aspirin-treated patients with low 11-dehydro-TXB2 excretion.Results: The 1 mL adapted method was highly correlated with the original assay (rho = 0.98, p < 0.001, n = 33).Both methods showed similar recoveries in samples spiked with exogenous 11-dehydro-TXB2. Urinary 11-dehydro-TXB2 values in samples immediately frozen were comparable and highly correlated to values in samples at4°C (day 6: rho = 0.99, p > 0.001, n = 8) or 25°C (day 6: rho = 0.98, p < 0.001, n = 23) up to 6 days in controls andpatients.Conclusions: Eleven-dehydro-TXB2 can be measured in small urine volumes and is relatively stable for a few daysafter collection, even at 25°C. These data allow the validation of this non-invasive cardiovascular biomarker inlarge studies.