Evaluation of a method to assess plasma viscosity: The falling ball viscometer

Abstract

Several methods are presently used to evaluate plasma viscosity and its variation. The falling ball viscometer, in spite of its cheap running cost, has been only used by a limited number of laboratories. We wish in this article to give our own appraisal of the technique. We studied the influence of the individual glass syringes and stainless steel balls, as well as the temperature dependence on plasma viscosity value. Freezing plasma samples did not appear to affect the value of plasma viscosity, as well as the mode and frequency of thawing, since the variations (0.01 mPa.s or less) were equivalent to the reliance of the technique (0.01 mPa.s, 1%). A reference range for healthy controls was determined. We could not detect any significant difference between men and women for plasma viscosity values. In spite of the fibrinogen increase with aging or smoking, we could not observe any significant variation for plasma viscosity values in healthy controls. However, in a large range of fibrinogen values, a good correlation was found between plasma viscosity and fibrinogen concentration (r² = 0.460; p = 0.0001). In 9 patients with IgG myeloma, a significant correlation between serum viscosity and IgG concentration was obtained (r² = 0.797; P = 0.001). Concomittant measurements of plasma viscosity with a rotational viscometer (Contraves LS30) showed a strong correlation with our values (r² = 0.980). We conclude that falling ball viscometry is a valid technique to measure plasma viscosity variations in clinical or research studies.