Blood viscosity--a comparative study on three rotational instruments.

Three rotational viscometers for blood viscometry were compared at moderate and high shear. At high shear, coefficients of variation were all around 1% increasing 5-fold (Wells-Brookfield) and 3-fold (Carri-Med) when shear was lowered. Using pathological samples the coefficients of variation for the Carri Med mashine was doubled. Only the Contraves LS-30 viscometer showed neither an increasing coefficient of variation with declining shear, nor problems when measuring blood with suspension instability.