Intrinsic factors that influence measurement of erythrocyte deformability.

The efficiency of rheological tests for measuring erythrocyte deformability is a function of test specificity and test sensitivity. Recent improvements in both specificity and sensitivity have revealed that rheological measurements of erythrocyte deformability are affected by the volume, haemoglobin concentration, and shape of the test erythrocytes. This applies both to filtration methods, using pores of 3-5 micron diameter, and to the measurement of erythrocyte elongation by laser diffractometry. Erythrocyte indices and morphology should therefore be measured routinely in both patients and controls so that the values for these intrinsic factors can be correlated with the results of rheological measurements in all published studies.