Long COVID is associated with elevated inflammatory and antibody levels. Elevated plasma proteins can increase blood viscosity and decrease blood flow. Our aim is to evaluate if blood viscosity is associated with long COVID outcomes. We conducted a cross-sectional study and included a sample of patients enrolled in our long COVID clinic. We estimated whole blood viscosity (WBV) using two previously validated formulas and compared it with the NASA lean test, COMPASS-31 scale as measures of dysautonomia and the symptom burden as measured by the modified COVID-19 Yorkshire scale. We obtained WBV at three different shear stress. We divided WBV and evaluated the distribution of symptom scores using univariate and multivariate models. We included 185 patients for this study. Our sample had a mean age of 56 ± 11 years, included 53% minorities and 32% were women. The mean C19-YRSm did not change with increasing tertile of WBV ( p > 0.05) while the mean COMPASS-31 score increased with increasing tertile of WBV in all levels of shear stress. In adjusted models the beta-coefficient of the C19-YRSm was (B -0.19p = 0.90) and for COMPASS-31 was (B 7.0 p = 0.01) for 208 s −1 and for all other levels of shear stress Twenty-three percent of patients in tertile 1 had either POTS or orthostatic hypotension compared to 32% on tertile 3 ( p = 0.04). Whole blood viscosity was associated with dysautonomia and not with long COVID symptoms.
Tamariz et al. (2026) studied this question.