Thromboxane A2 (TXA2), produced from arachidonic acid, causes irreversible platelet aggregation, vascular, and bronchial smooth muscle contraction. TXA2 is rapidly hydrolyzed non-enzymatically to form TXB2. However, most of the TXB2 measured in the plasma or urine of healthy individuals is due to ex vivo platelet activation or intra-renal production, and normal concentrations of circulating TXB2 are extremely low (1-2 pg/ml) and highly transient (t½ = 5-7 minutes). 11-dehydro TXB2 is a metabolite of TXB2 (not formed by platelets or the kidney) with a circulating half-life (t½) of 45 minutes. Its measurement in plasma or urine will give a time-integrated indication of TXA2 production and is recommended to estimate TXA2 levels to circumvent measurement complications associated with TXB2. Cayman’s 11-dehydro TXB2 ELISA Kit is a competitive assay that can be used for quantification of 11-dehydro TXB2 in urine and other sample matrices. Normal plasma levels of 11-dehydro TXB2 (1-2 pg/ml) are below the detection limit of this assay (16 pg/ml), so plasma samples must be purified and concentrated prior to analysis. Urine samples should be diluted appropriately before assaying. There is evidence suggesting that 11-dehydro TXB2 can be formed non-enzymatically following platelet activation, so it is important to process plasma samples quickly to prevent artifactual formation of 11-dehydro TXB2. The assay has a range from 15.6-2,000 pg/ml and a sensitivity (80% B/B0) of approximately 34 pg/ml.