Whole blood viscosity in plasma cell dyscrasias

Plasma or serum hyperviscosity in plasma cell dyscrasias (PCD) has been described as a risk factor for circulatory disturbances. Whole blood viscosity (WBV) would theoretically be a better biomarker but has not been studied in PCD.Plasma viscosity (PV) and WBV were measured in 89 subjects with PCD and in 60 healthy blood donors by free oscillation rheometry. A complete blood count was obtained using an automated hematology analyzer. Plasma proteins were quantitated by immunoturbidimetry.The reference intervals for menwomen were 1.16-1.361.16-1.38 mPa for PV, and 4.9-6.34.4-6.2 mPa for WBV, respectively. Of the PCD patients, 71% had PV above the reference limit and 40% were above the WBV limit. Multivariate analysis showed that WBV was independently related to hematocrit, PV, concentration of the monoclonal protein (M-protein), plasma fibrinogen concentration and albumin concentration. This model accounted for 76% of the variance in WBV. When the same model was applied to PV, only the concentration of the M-protein was significantly related and the model accounted only for 20% of the variance in PV.PV cannot be used as a surrogate marker for WBV in PCD patients. Whole blood viscosity should replace plasma viscosity in patients with PCD.