Western blot analysis of GP Ibα in platelet lysates and plasma. GP Ibα or its degradation products in the patient's platelets and platelet-poor plasma were analyzed by immunoblotting with the GP Ibα antibody WM-23. Platelets from the patient (P) and from an unaffected control subject (N) were prepared from an equal volume of PRP. Platelet lysates were compared for GP Ibα content (left panel) and GP IIb content (middle panel, antibody G1.9). N/5 represents a fivefold dilution of the normal plasma. The right panel is an immunoblot of 20 μL normal plasma and patient plasma.