A test of the ability of platelets to occlude a small aperture when whole blood is forced through it under conditions of high shear stress. The time required for blood to occlude the aperture of the test device is known as the closure time. The test is used to evaluate diseases and conditions in which platelets may function abnormally, e.g., in menstruating women with menorrhagia or in patients sdiussepaescet. ed of having von Willebrand’s disease.