The template bleeding time is still the screening test for defects of platelet function, although it is an invasive and poorly reproducible technique. The PFA-100 measures platelet function at high shear. Whole blood is aspirated through a capillary to an aperture of a membrane coated with platelet agonists. The system measures the time required to obtain occlusion of the aperture by a platelet plug (closure time). We measured the closure times in the PFA-100 system and the bleeding time in seven patients with delta-
storage pool deficiency, 10 patients with "primary secretion defect" (not due to abnormalities of platelet granules or the arachidonate pathway), and 40 controls. Measurements were repeated I and 4 hours after
intravenous infusion of
desmopressin in six delta-
storage pool deficiency and eight primary secretion defect patients. Baseline bleeding time and closure times with the
collagen/
epinephrine cartridge were longer in delta-
storage pool deficiency and primary secretion defect patients than in controls. In contrast, closure times with the
collagen/
adenosine diphosphate cartridge were normal in both delta-
storage pool deficiency and primary secretion defect patients. Treatment with
desmopressin increased the plasma
von Willebrand Factor levels, shortened the prolonged bleeding time, shortened the closure times with the
collagen/
adenosine diphosphate cartridge, and normalized the closure times with the
collagen/
epinephrine cartridge. Therefore, the PFA-100 test may be a less invasive alternative to the bleeding time in the diagnosis and therapeutic monitoring of patients with platelet secretion defects. The
collagen/
epinephrine cartridge is more sensitive than the
collagen/
adenosine diphosphate cartridge to defects of platelet secretion.