Blood Viscosity and Mortality in Patients Hospitalized With COVID-19

Quick Takes

  • Elevated blood viscosity has been hypothesized to contribute to adverse events in moderate–severe COVID-19 beyond traditional risk factors.
  • Higher blood viscosity is associated with a significantly elevated risk of in-hospital mortality for patients with COVID-19.
  • The increased risk of in-hospital mortality persisted even in the subgroup of patients without cardiopulmonary comorbidities.

Study Questions:

What is the association between estimated blood viscosity and mortality among hospitalized patients with coronavirus disease 2019 (COVID-19)?


The authors included 5,621 patients hospitalized with COVID-19 at Mount Sinai Health System between February 27, 2020–November 27, 2021. Estimated blood viscosity was calculated using the Walburn-Schneck model, and multivariable Cox models were used to evaluate the association between blood viscosity and in-hospital mortality. The models were adjusted for demographics, comorbidities, in-hospital pharmacotherapy, and baseline inflammatory markers.


Estimated blood viscosity was associated with increased in-hospital mortality using two different measures. One-centipoise increase in high-shear blood viscosity was associated with a 36.0% relative increase in death (p < 0.001). A similar increase in low-shear blood viscosity was associated with a 7.0% relative increase in death (p < 0.001). Compared to participants in the lowest quartile of high-shear blood viscosity, those in the highest quartile had a higher mortality (adjusted hazard ratio [aHR], 1.53; 95% confidence interval [CI], 1.27-1.84), including the subgroup of patients without any comorbidities (aHR, 1.69; 95% CI, 1.28-2.22).


The authors concluded that increased blood viscosity is associated with higher in-hospital mortality for patients hospitalized with COVID-19.


COVID-19 is associated with both a higher mortality and thromboembolic risk than other coronavirus infections. Experts have hypothesized that COVID-19 infection was associated with increased blood viscosity, resulting from a complex set of rheologic mediators beyond coagulation cascade activation. These data suggest that elevated blood viscosity may strongly predict in-hospital outcomes, even among patients with few/no comorbidities. While not traditionally assessed by front-line clinicians, viscosity can be estimated with readily available laboratory values (hematocrit, albumin, and total protein). However, without targeted therapeutics, the utility of this clinical measure remains to be defined in routine practice.

Clinical Topics: COVID-19 Hub, Geriatric Cardiology, Heart Failure and Cardiomyopathies, Prevention

Keywords: Albumins, Blood Coagulation, Blood Viscosity, Comorbidity, Coronavirus Infections, COVID-19, Drug Therapy, Geriatrics, Hematocrit, Hospital Mortality, Inflammation Mediators, Risk Assessment, Secondary Prevention, Thromboembolism, Vascular Diseases, Viscosity

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