Aspirin resistance among long-term aspirin users after carotid endarterectomy and controls: flow cytometric measurement of aspirin-induced platelet inhibition.

BACKGROUND: Numerous studies have indicated that some patient subpopulations do not respond to the antithrombotic effects of aspirin. The objective of this study was to evaluate aspirin-induced inhibition of platelet cyclooxygenase (COX) using a flow cytometric technique in long-term aspirin users after carotid endarterectomy (CEA) and controls with newly diagnosed carotid stenosis not taking aspirin and to compare these results with platelet function analyzer measurements. METHODS: The study included 86 patients with a history of CEA on long-term aspirin therapy (100 mg daily) and 29 age-matched patients with newly diagnosed carotid artery stenosis not taking aspirin. Platelet-rich plasma diluted with phosphate-buffered saline was incubated with arachidonic acid (ARA) at a final concentration of 80 micromol/L. After staining with phycoerythrin-labeled anti-P-selectin (CD62p) antibody, platelet CD62p-antigen expression was measured on a flow cytometer. RESULTS: Flow cytometric measurement of ARA-induced platelet activation showed an inhibition of ARA-induced platelet stimulation in all patients on aspirin therapy, whereas all but two controls (95%) showed expected platelet reactivity. In contrast, results of the platelet function analyzer measurements were normal in 16% of aspirin-treated patients. CONCLUSIONS: Flow cytometric measurement of CD62p expression on platelets after incubation with ARA proved to be a practicable tool to monitor aspirin-induced inhibition of platelet COX. Results in patients on long-term low-dose aspirin therapy show that the inability of aspirin to inhibit platelet COX for both symptomatic and asymptomatic patients with high-grade internal carotid artery stenosis is a very rare event. So-called aspirin resistance detected quite frequently by platelet function analyzer measurement is most likely from COX-independent mechanisms.

Lupus anticoagulant in patients with chronic venous insufficiency.

Chronic venous insufficiency is a widespread disease that can often lead to venous leg ulcers. Recent studies report that certain clotting abnormalities, such as anticardiolipin antibodies, are associated with leg ulcers. Although lupus anticoagulant belongs to the antiphospholipid antibodies, its presence in patients with chronic venous insufficiency has not been reported previously. The purpose of our study was to determine the presence of lupus anticoagulant in chronic venous insufficiency patients at a stage with no leg ulcers, and to follow the clinical outcome. In 37 patients with chronic venous insufficiency and in 54 control patients, lupus anticoagulant was evaluated using the Viper Venom Russell's Diluted Test. Lupus anticoagulant was found significantly more often (p < 0.001) in patients with chronic venous insufficiency than in controls. After 4 years, patients with chronic venous insufficiency with lupus anticoagulant were found to develop a venous leg ulceration more frequently compared to those without (p = 0.01), suggesting that lupus anticoagulant may play an important role in the pathogenesis of chronic venous insufficiency.