Serum Thromboxane B2 Compared to Five Other Platelet Function Tests for the Evaluation of Aspirin Effect in Stable Cardiovascular Disease

BackgroundTo assess the role of serum thromboxane B2 (TXB2) measurements and the correlation between platelet function studies, in patients with stable cardiovascular disease on aspirin or clopidogrel.Methods76 patients (47 on aspirin, 16 clopidogrel, 13 both) underwent assessment of TXB2, whole blood aggregometry (WBA) after stimulation with (i) arachidonic acid (0.5 mM), (ii) ADP (5 μM), (iii) collagen (1 and 5 μg/ml), PFA-100®, and Cone and Plate Analyzer. Clopidogrel patients were additionally assessed by the VerifyNow® System.ResultsTXB2 values ranged between 0.2 and 56.2 ng/ml, with significant separation between those taking aspirin, clopidogrel and controls (0.45 ng/ml vs 6.85 ng/ml vs 12.97 ng/ml, p < 0.001). There was moderate correlation between WBA-AA and TXB2 (r = 0.487, p < 0.001), PFA-100® (r = 0.599, p < 0.001), WBA-Col1 (r = 0.424, p < 0.001), WBA-Col1:5 (r = 0.417, p < 0.001), and between TXB2 and PFA-100® (r = 0.509, p < 0.001). The prevalence of aspirin non-responders for WBA-AA, TXB2, PFA-100®, CPA and Coll1:5 was 13.1%, 8.2%, 14.8%, 9.7% and 16.4% respectively. Individual patients were not consistently classified as aspirin non-responders in all tests. Those with inadequate aspirin response on ≥3 tests had higher TXB2 levels (mean 1.57 ± 1.66, range 0.553–4.45 vs mean 0.45 ± 0.18, range 0.23–1.50) (p = 0.001).Clopidogrel suppressed TXB2 (p = 0.02), WBA-AA (p < 0.001), WBA-Col1 (p = 0.012) and WBA-ADP (p < 0.001) compared to controls. TXB2 in patients ingesting fish oil tablets was lower compared to those without (0.4 ng/ml vs 0.52 ng/ml, p = 0.004). Obesity was associated with higher TXB2 values (0.61 vs 0.41, p = 0.01).ConclusionSerum TXB2 measurements are a direct measure of the pharmacological effect of aspirin, are easily performed and correlate with other measures of platelet function. Serum TXB2 measurements could be a useful sole measure of aspirin non-response, and may be even more predictive when performed in tandem with a global measure of platelet function. Aspirin and clopidogrel both suppressed several platelet pathways.