How should blood rheology be measured in macroglobulinaemia?

Blood and plasma viscosity were measured in 13 patients with monoclonal macroglobulinaemia. Blood viscosity was measured at natural hematocrit and after adjustment to 45%. Studies were performed at three different temperatures, +24 degrees C, +32 degrees C and +37 degrees C. Plasma viscosity was measured in a rotational viscometer and in a capillary tube at the above-mentioned temperatures. Blood viscosity was to some extent related to the patients' symptoms, whereas a correlation between blood and plasma viscosity became less pronounced with decreasing shear rates, indicating that plasma viscosity is not a perfect indicator of blood viscosity in macroglobulinaemia. It was shown that red cell concentration, besides the concentration of monoclonal immunoglobulins (= paraproteins (PP)), is an important determinant of blood viscosity. The correlation between red cell concentration and viscosity became stronger with decreasing shear rate. Whole blood viscosity at low shear rates seems to be the best indicator of rheological symptoms in patients with macroglobulinaemia. It is concluded that blood rheology in patients with macroglobulinaemia is best studied at +32 degrees C to +37 degrees C in whole blood and at low shear rates.