Distribution of blood viscosity values and biochemical correlates in healthy adults.

Increases in the viscosity of blood and plasma predict clinical manifestations of atherothrombotic vascular disease. The clinical utility of viscosity measurements in cardiovascular risk factor analysis requires reference values established from a healthy disease-free population. A cohort of 126 (71 men, 55 women) healthy nonsmoking adults had fasting blood analysis after a 12-14-h fast. Viscosity measurements were made on samples of whole blood, plasma, and serum at 37 degrees C with a coaxial cylinder microviscometer. The mean blood viscosity at shear rates of 100, 50, and 1 s-1 were 3.26 +/- 0.43, 4.37 +/- 0.60, and 5.46 +/- 0.84 mPa.s, respectively. Men had significantly higher blood viscosity values than women at each shear rate. The differences in blood viscosity did not remain significant after blood viscosity values were normalized to a hematocrit of 45%, except at 100 s-1. For the entire group, normalized blood viscosity values at each measured rate correlated inversely with HDL cholesterol and positively with fibrinogen. The mean plasma viscosity was 1.39 +/- 0.08 mPa.s and the mean serum viscosity was 1.27 +/- 0.06 mPa.s. Plasma viscosity correlated with fibrinogen (r = 0.51, P < 0.0001), total serum protein (r = 0.33, P < 0.0001), and triglyceride concentrations (r = 0.33, P < 0.0015). Serum viscosity correlated with total serum protein (r = 0.50, P < 0.0001) and LDL cholesterol (r = 0.24, P = 0.0065). This study provides reference values for the viscosity of blood, plasma, and serum that may assist in evaluating hemorheological profiles.