Summary
Some patients with thrombocytosis due to myeloproliferative diseases or other etiologies
experience thromboembolic complications and others may bleed excessively. It seems
unlikely that elevations in platelet count per se are a direct cause either of thrombosis or of hemorrhage. In an effort to ascertain
whether variations in platelet function might determine whether an individual patient
experiences thrombotic or hemorrhagic complications we have evaluated platelet function
in 22patients with thrombocytosis due to a variety of etiologies. The results of platelet
counts, bleeding time determinations, and studies of platelet aggregation were similar
in patients with thrombosis, in patients with bleeding and in patients with neither
complication. Therefore, detailed studies of platelet coagulant activities were carried
out in 8patients. The results of platelet coagulant activity assays were normal in
all 3patients with thrombocytosis and neither thrombotic nor bleeding complications
and an additional 3patients with myeloproliferative diseases, normal platelet counts
and no thrombohemorrhagic complications. In 2patients with thrombotic complications
significant elevation of platelet coagulant activities concerned with the early phases
of intrinsic coagulation were observed whereas in 2patients with severe hemorrhagic
complications deficiences of either contact forming activity or collagen-induced coagulant
activities were evident. This preliminary study suggests the possibility that variations
in platelet coagulant activities concerned with the early stages of intrinsic coagulation
may determine whether patients with thrombocytosis will experience bleeding or thrombotic
complications.
