Morphologic alterations of blood cells in the impedance aggregometer

The scanning (SEM) and transmission (TEM) electron microscopic appearance of blood cells was studied in correlation with the aggregometer tracing recorded after activation of whole blood samples by collagen or ADP. Early morphologic alterations of platelets characterized by the formation of marginal pseudopods and bulbous protrusions were not indicated by the aggregometer. The initial increase in impedance was caused by the attachment of platelets displaying typical shape change morphology at the surface of the electrode wires joint with collagenous fibrils in collagen activated specimens. During further increase in impedance, aggregates were detectable in the blood suspension and at the electrode, the number and size of which increased up to the maximal extension of the aggregometer tracing. Using low doses of ADP (2-3 microM), dissociation of aggregates in the blood suspension was detectable by SEM, which was not recorded by the aggregometer tracing indicating further limitation of the impedance aggregometer. In collagen activated samples, platelet aggregates were covered by PMN and monocytes that in TEM displayed distinct phagocytosis of platelet fragments and fibrin masses. In ADP specimens, activation of leukocytes was only rarely detectable. The detection of mixed aggregates may be important for further employment of the impedance aggregometer in the diagnosis of hematologic diseases.