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Stability of Urinary Thromboxane A2 Metabolites and Adaptation of the Extraction Method to Small Urine Volume by Francesca Pagliaccia, Aida Habib, Dario Pitocco, Giovanna Petrucci, Francesco Zaccardi, Enrico Di Stasio, Bianca Rocca

Background: Thromboxane (TX) A2 is a pro-thrombotic prostanoid synthesized by activated platelets, biotransformed into 11-dehydro-TXB2, measurable in urines. Eleven-dehydro-TXB2 excretion is increased in high risk cardiovascular diseases; however, this cardiovascular biomarker awaits validation in large trials. The need of large urine volume (8 - 10 mL) and the unknown stability of 11-dehydro-TXB2 in urine after collection might limit its 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 also tested 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 at 4°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 and patients.
Conclusions: Eleven-dehydro-TXB2 can be measured in small urine volumes and is relatively stable for a few days after collection, even at 25°C. These data allow the validation of this non-invasive cardiovascular biomarker in large studies.

DOI: 10.7754/Clin.Lab.2013.121238