Essential athrombia: study of a new case.

A constitutional platelet function disorder in a twelve year-old girl characterized by a lifelong bleeding tendency, prolonged bleeding time, normal platelet count, normal clot retraction, normal platelet factor 3 activity and impaired platelet aggregation was reported. Platelet aggregation, studied turbidimetrically, was absent in the presence of usual doses of ADP (1-4 MUM) although a small wave of primary aggregation was obtained by very large ADP concentrations (25-50 muM). The platelets were also unresponsive to epinephrine, thrombin and diluted collagen suspensions.