Summary
The results of assaying platelet coagulant activities in a patient with clinically
mild thrombasthenia are compared with those previously reported in 4 patients with
clinically severe and 2 patients with moderately severe thrombasthenia. Contact product
forming activity and platelet factor 3 activity were normal in the present patient,
and decreased in the more severely affected patients. Intrinsic factor-Xa forming
activity was normal or supranormal in all patients. Collagen-induced coagulant activity
was present in mildly and moderately affected patients and absent in severely affected
patients. The present patient would appear to possess both alternative mechanisms
by which platelets can initiate intrinsic clotting, compared to the moderately affected
patients who lack one and the severely affected patients who lack both pathways. Although
the present patient’s platelets failed to aggregate in response to ADP they responded
normally to ADP in the assay for contact product forming activity.
