PLASMA INHIBITOR OF PLATELET FUNCTION IN β-THALASSEMIA

Abstract

Patients with homozygous B-thalassemia of ten have moderate to severe epistaxis and/or a petechial rash with normal platelet count, PT and PTT. For this reason we have studied platelet function (P1 F). Pre-transfusion evaluation included: Duke bleeding time (BT), PF₃ release (Stypven), aggregation (epinephrine, ADP, collagen), PT, PTT and platelet count. PI F was abnormal in 13/30 patients(43%) studied: 10/13 had recurrent epistaxis and/or petechial rashes. 3 had minimal symptoms; 13/13 had abnormal aggregation with epinephrine, 10/13 with ADP, and 10/13 with collagen; only 1 also had slightly low PF₃ release; BT was abnormal in 3/13. At time of study platelet count was normal in all, PT and PTT in most; none were receiving anti-aggregating drugs. Patients' platelets were isolated, washed by Ardlie buffer method, lysed and analyzed spectophotomet-rically for iron. No iron deposition in platelets was detected by this method. In other experiments, donor platelets were washed or gel-filtered to render them free of donor plasma; test plasma was then added to platelets and platelet aggregation assays were performed. Normal donor platelets were abnormal when tested in plasma from patients with abnormal P1 F; platelets from 3 patients with abnormal P1 F functioned normally in normal plasma but abnormally in “abnormal” plasma. Abnormalities of platelet aggregation are detectable in 1/2 symptomatic patients. Our data suggest that the P1 F abnormalities detected in β-thalassemia may be due to a plasma Inhibitor, rather than an intrinsic platelet defect.

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