Blood viscosity in hyperthyroidism: Significance of erythrocyte changes and hematocrit

Abstract

Blood viscosity was measured in 16 hyperthyroid patients before and after normalization of thyroid function, at natural hematocrit (8 patients) and with the hematocrit of the samples adjusted to 40 and/or 45%. In 10 of the patients the passage time for erythrocytes through a cellulose-sigmacell column was also measured.

With the hematocrit adjusted to 45% a higher (p < 0.01) blood viscosity was recorded for patients compared to 33 controls at shear rates 0.8 s⁻¹–40 s⁻¹. After treatment it decreased (p < 0.05) to a level close to that of controls. Also blood viscosity at hematocrit 40% decreased upon treatment for hyperthyroidism. The plasma viscosity in the patients did not differ significantly from controls and did not change significantly after treatment for hyperthyroidism. The column passage time was longer for erythrocytes from hyperthyroid patients than controls, and was correlated (p < 0.01) to blood viscosity at hematocrit 45% at all shear rates investigated (r=0.61–0.72). The hematocrit increased from 38.9±3.8 (SD) to 42.1±3.3 % (p < 0.01) after treatment for hyperthyroidism. It is concluded that in hyperthyroidism the erythrocytes may be decreased in concentration and changed in a way that impairs their rheological properties. A normalization is seen upon treatment of the disease.