Glanzmann thrombasthenia is a rare autosomal recessive disorder with defective platelet aggregation from deficiency or dysfunction of glycoprotein IIb/IIIa. The platelet aggregation studies described here are characteristic of this disorder. Disseminated intravascular coagulation results in the consumption of all coagulation factors and platelets, so the prothrombin time and partial thromboplastin time are elevated with thrombocytopenia. Immune thrombocytopenic purpura is caused by antibodies to platelet membrane glycoproteins IIb/IIIa or Ib/IX. Scurvy resulting from vitamin C deficiency causes bleeding into soft tissues and skin from increased capillary fragility, but platelet number and function are normal. Von Willebrand disease is one of the most common bleeding disorders and results from qualitative or quantitative defects in von Willebrand factor.