Platelet function and morphologic characteristics were evaluated in 43 patients with myeloproliferative disease (MPD), 5 patients with myelodysplastic syndrome (MDS), and 7 patients with secondary thrombocytosis (ST). Platelet Factor IV (PF4) and B-thromboglobulin (BTG) showed slight elevation in ST but significant elevation in all MPDs. They were either normal or slightly elevated in MDS. Defective platelet aggregation with one or more inducers was seen in 62% of all patients. An epinephrine-induced defect was the most consistent aggregation abnormality. Hyperaggregation and spontaneous aggregation were seen in 15% of patients. Of the eight patients who showed increased bleeding tendency, all eight showed defective aggregation with two or more inducers, five showed decreased surface activation response, as well as decreased or abnormal granules and dense tubular disarray in the transmission electron microscope (TEM) study. Seven patients had clinical evidence of recurrent arterial and venous thromboses. Five of these patients showed hyperaggregation response to adenosine diphosphate and collagen and abnormal Wu and Hoak platelet aggregate ratio. Four patients showed spontaneous aggregation on aggregometer. Surface activation response was significantly increased in five patients, and an increase in platelet granules by TEM study was seen in four patients. Primary thrombocythemia could be differentiated from secondary thrombocytosis (ST) by the presence of abnormal aggregation response and significantly increased PF4 and BTG in the former, and greatly elevated plasma fibrinogen and Factor VIII, as part of acute phase reactant response, in the latter.

Two patients with essential thrombocythemia showed a marked decrease in ristocetin-induced platelet aggregation in addition to other aggregation defects during routine aggregation studies for prolonged bleeding times. Further investigation revealed type I von Willebrand's disease (vWD) in one patient and a variant of vWD compatible with type IIA defect in the second patient. The latter patient had minor episodes of epistaxis clinically, while the patient with type I disease experienced excessive blood loss during menstrual periods. Both patients gave negative history for abnormal bleeding in the past or in their families. Both have had uneventful surgical procedures in the past, at which time bleeding times and basic coagulation test results were normal.

A 37-year-old intravenous drug abuser with acquired immune deficiency syndrome showed elevated activated partial thromboplastin time (APTT) and prothrombin time, normal thrombin time and fibrinogen, and borderline low platelet counts. The patient subsequently had a fracture of the left zygomatic arch, which did not produce uncontrollable bleeding. The coagulogram repeated at this admission showed persistent elevation of APTT. Further coagulation workup showed the presence of a lupus anticoagulant with mild specific inhibition of Factor VII. Platelet aggregation and Factor II levels were normal.

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