Platelet activation with unfractionated heparin at therapeutic concentrations and comparison with low-molecular-weight heparin and with a direct thrombin inhibitor.

To the Editor: We read with interest the article by Xiao and Theroux1 on “Platelet Activation With Unfractionated Heparin at Therapeutic Concentrations and Comparisons With a Low-Molecular-Weight Heparin and a Direct Thrombin Inhibitor.” They found that platelets of patients with unstable angina were hyperresponsive during treatment with unfractionated heparin (UFH). Moreover, aggregation to ADP and thrombin receptor agonist peptide (TRAP) was enhanced after addition of UFH ex vivo to blood of normal volunteers. In contrast, when a low-molecular-weight heparin …