Objectives: The aim of this study is to clarify whether increased aggregation of red blood cells (RBCs) of multiple myeloma (MM) patients is caused by changes in plasma chemical composition or is associated with alterations in RBC properties and in addition, to suggest an approach to revert the enhanced aggregation in MM toward normal.
Materials and methods: 40 blood samples of MM patients and suspensions of control RBCs in MM plasma were examined. In addition, RBC aggregation in MM blood was studied in the presence of dextrans with mean molecular weights of 9.6 and 40 kDa (D9.6 and D40). A method based on electrical and dielectric properties of cellular suspensions was used to study RBC aggregation. In this method, a lower aggregation index demonstrates a higher aggregability.
Results: The mean values of aggregation index for whole blood of healthy individuals, control cells in MM plasma and MM blood sample are 19.0, 7.2 and 3.2%, respectively. The kinetics of RBC aggregation slow down with the decrease in the fraction of MM plasma. No correlation was found between RBC aggregation and the immunoglobulin plasma level. Addition of D9.6 to MM blood reverts the enhanced aggregation toward normal.
Discussion: The findings that RBC aggregation changes in the following order: MM blood > normal RBCs in MM plasma > control blood sample, suggest that surface-active plasma molecules play a role in enhanced aggregation in MM. The surface concentration of these molecules and hence RBC aggregability is reduced in the presence of dextrans due to their competitive adsorption onto RBC membrane. Because the end-to-end distance of D40 is quite comparable with the Debye length, the effect of this particular dextran on RBC aggregation is negligible.