White cell retention compared with platelet retention in the filterometer: controls and abnormal states

Platelets and white cells contribute to thrombus formation. In the filterometer, platelet retention in normal citrated blood increases from 47.5% at 0-5 s to 81.5% at 20-40 s. White cell retention is normally closely related to platelet retention at 0-5 s but less so at 20-40 s. However at 20-40 s the number of white blood cells (WBC) retained has decreased relative to 0-5 s. This apparent paradox is now further explored using antibodies to glycoprotein (GP) Ib, to von willebrand factor (vWf) and to GPIIb-IIIa together with observations on a number of clinical conditions with abnormal platelet retention. In citrated blood, platelet retention of 0-5 s was significantly decreased relative to normal in von Willebrand's disease, in aortic valve stenosis and with the addition of anti-vWf-GPIb and minimally with anti-GPIIb-IIIa antibodies. WBC retention of 0-5 s in these groups was always 41 2%. However when platelet retention 0-5 s was raised (pregnancy and venous occlusion), white cell retention was also raised. At 20-40 s in all the nine conditions studied, the white cell and platelet retention were closely related, but the percentage WBC retained decreased relative to the platelet retention. Granulocyte retention was higher than lymphocyte retention, but both cell types were similarly affected. We conclude that the platelets are retained as previously described. The white cells (all types) initially bind at least in part in an independent unexplained way (0-5 s). Thereafter the degree of platelet activity (retention %) largely determines the degree of WBC retention. This is probably due to a proportional amount of P-selectin liberated by the activated platelets.