Measuring Deformability and Red Cell Heterogeneity in Blood by Ektacytometry

Decreased red cell deformabilityis characteristic of several disorders. In some cases, the extent of defective deformabilitycan predict severity of disease or occurrence of serious complications. Ektacytometry uses laser diffraction viscometry to measure the deformabilityof red blood cells subject to either increasing shear stress or an osmotic gradient at a constant value of applied shear stress. However, direct deformabilitymeasurements are difficult to interpret when measuring heterogenous blood that is characterized by the presence of both rigid and deformable red cells. This is due to the inability of rigid cells to properly align in response to shear stress and results in a distorted diffraction pattern marked by an exaggerated decrease in apparent deformability. Measurement of the degree of distortion provides an indicator of the heterogeneity of the erythrocytes in blood. In sickle cell anemia, this is correlated with the percentage of rigid cells, which reflects the hemoglobin concentration and hemoglobin composition of the erythrocytes. In addition to measuring deformability, osmotic gradient ektacytometry provides information about the osmotic fragility and hydration status of erythrocytes. These parameters also reflect the hemoglobin composition of red blood cells from sickle cellpatients. Ektacytometry measures deformabilityin populations of red cellsand does not, therefore, provide information on the deformabilityor mechanical properties of individual erythrocytes. Regardless, the goal of the techniques described herein is to provide a convenient and reliable method for measuring the deformabilityand cellular heterogeneity of blood. These techniques may be useful for monitoring temporal changes, as well as disease progression and response to therapeutic intervention in several disorders. Sickle cell anemiais one well-characterized example. Other potential disorders where measurements of red cell deformabilityand/or heterogeneity are of interest include blood storage, diabetes, Plasmodium infection, iron deficiency, and the hemolytic anemiasdue to membrane defects.