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© Dirk Biddle
Plasma viscosity is affected by the concentration of large plasma proteins, particularly those with pronounced axial asymmetry - fibrinogen and some immunoglobulins. Lower levels of plasma viscosity are seen in neonates because of lower levels of proteins, particularly fibrinogen. There is a slight increase in viscosity in the elderly as fibrinogen increases. There is no difference between males and females. Plasma viscosity is not affected by anaemia (unlike ESR) or red blood cell size.
Major shifts in the viscoelasticity of blood have been found to be associated with such pathologies as myocardial infarction, peripheral vascular disease, cancer and diabetes (1).
The test is expensive, not widely available, and technically cumbersome to perform. The most common method of determining the consistency of a flowing liquid uses the relation between shear stress and time rate of shear strain (or shear rate). If the flow is constant in time, then the ratio of shear stress to shear rate is the viscosity. When flows are changing with time, such as blood flow in the human circulation, the liquid generally demonstrates both a viscous and an elastic effect, both of which determine the stress-to-strain rate relationship. Such liquids are called viscoelastic. Blood plasma normally shows viscosity only, while whole blood is both viscous and elastic (2).
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1 http://www.vilastic.com/tech10.html
2 Lowe, G. and Barbenel, J. (1998) Plasma and blood viscosity. Clinical Blood Rheology, 1, 11-44.