Hemorrheological approach to thrombotic microangiopathies.

Microangiopathic hemolytic anemia is a typical hematological feature of the syndromes characterized by thrombotic microangiopathy as histopathological lesion (hemolytic uremic syndrome and thrombotic thrombocytopenic purpura). Nevertheless endothelial lesions alone do not account for all morphologic red cell abnormalities seen in the blood smear, which cannot be explained only by mechanical damage. At least some of these erythrocytic alterations can be traced to primitive erythrocyte damage (by intrinsic or extrinsic toxic causes) responsible for a hemorrheological unbalance capable of participating in the pathogenetic mechanisms involved. Deformed and fragmented poorly deformable red cells can contribute by themselves to microcirculatory impairment, leading to endocapillary engorgement, increase of peripheral resistances and endothelial damage.