The commonest cause of hyperviscosity syndrome is increased IgM in patients with of Waldenström’s macroglobulinaemia. Clinically significant increases in viscosity are most common in patients with increased immunoglobulin, both monoclonal and polyclonal.
Of the plasma constituents immunoglobulins and cholesterol are clinically relevant. Acute phase reactants increase plasma viscosity. Fibrous proteins like fibrinogen contribute more to plasma viscosity than globular proteins like albumin. Plasma viscosity varies with the concentration of its constituents. Blood viscosity depends on plasma viscosity and the type and number if blood cells. The increase is dramatic at low shear rates. The viscosity of blood, a non-Newtonian fluid, Blood viscosity increases with falling shear rates. The viscosity of Newtonian fluids like water, honey and oil does not change with flow rates. Depending on whether the viscosity of fluids changes with flow rate or not fluids may be Newtonian of non-Newtonian. The higher the viscosity, thicker the fluid. Viscosity, the internal friction between these layers, is a measure of thickness of a fluid. During laminar flow the layer closest to the wall is the slowest and the layer farthest, fastest. The flow may be laminar flow that is orderly in parallel layers or turbulent flow that is chaotic.
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