Plasma is a Newtonian fluid because:
For a Newtonian fluid, viscosity remains constant, independent of the shearing force. Whole blood is a non-Newtonian fluid; its viscosity goes changing with the changes in shearing force.
Viscosity is directly propoional to shear stress
Viscosity is equal to shear stress
Viscosity is inversely related to shear stress
Viscosity is independent of shear stress
Blood Physiology