title: Comparative evaluation of two newly developed devices for capillary viscometry.
abstract: Viscometry is an often applied method in clinical chemistry. A variety of studies demonstrate an association of parameters related to blood viscosity with human pathology of varying origin. Whole blood and plasma viscosity are considered to be clinically useful indicators in the diagnostic workup and therapy monitoring of certain diseases. In this study, we compare the "Waegeviskosimeter" (WV) described in previous publications with a newly developed device, the "Reverse Flow Viscometer" (RFV). Both viscometers are capillary flow viscometers. Both overcome the disadvantage of common viscometers of the Ubbelohde and Cannon-Fenske type which require large amounts of plasma and which can be only applied to Newtonian fluids. The accuracy of the measurements of both viscometers, requiring less than 1.0 ml sample volume, is superior to most conventional methods. The major distinction in the functionality of the WV and the RFV is that the WV measures the kinematic viscosity whereas the RFV directly estimates dynamic viscosity without the requirement of additional density measurement. We found good reproducibility of viscosity with coefficient of variation CV < or =1.1% for both viscometers. Quality assurance measures have been carried out. Because no quality assurance scheme according to the guidelines proposed by the German Medical Association exists for plasma or whole blood viscosity, we tested reference material Lyphochek Unassayed Chemistry Control Level 1 and Level 2 (Bio-Rad Laboratories). We determined the viscosities 1.40 mPa s and 1.08 mPa s (37 degrees C) and the between-run precision from daily quality control runs with CV of 1.4% and 1.2% for the WV, and 1.7% and 1.4% for the RFV. For direct comparison reasons, we determined the viscosity in seventy human plasma and serum samples by both methods. Using the regression analysis described by Passing-Bablok, the RFV and the WV methods are highly correlated and show only little variations (r = 0.990, tau = 0.896). The regression equation is y(WV) = 1.035x(RFV) - 0.056 with a mean deviation of 0.4+/-3.6%. We conclude that both new devices for viscosity assessment fulfill all quality requirements as prescribed for clinical chemical laboratories. One advantage RFV is to measure the dynamic viscosity directly.
authors.affiliation: Institute of Clinical Chemistry and Laboratory Medicine, University of Rostock, Medical Faculty, Germany. birgit.holdt@med.uni-rostock.de
authors.forename: Birgit
authors.initials: B
authors.lastname: Holdt
authors.forename: Jochen K
authors.initials: JK
authors.lastname: Lehmann
authors.forename: Peter
authors.initials: P
authors.lastname: Schuff-Werner
mesh_terms: D001809:Blood Viscosity; D018056:Hemorheology / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D006801:Humans; D012015:Reference Standards; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity