Patients hospitalised with COVID-19 who have a high estimated blood viscosity are more likely to die from complications. High blood viscosity reduces blood flow to small vessels and raises the risk of blood clots. This blood thickness measurement can be used to predict mortality.

This study was published in the Journal of the American College of Cardiology. This is the first large-scale study to look at blood viscosity as a predictor of mortality in COVID-19 patients.

When compared to common measures of inflammation and the blood clotting biomarker D-dimer, a simple calculation of blood viscosity was more robust in identifying hospitalised patients at risk of dying from COVID-19 complications.

Doctors typically measure hematocrit and globulins (the difference between total protein and albumin) in all patients for diagnosis and monitoring treatment of hospitalised patients; however, blood viscosity is not directly measured.

The hematocrit and globulins can be used to calculate blood viscosity. In this study, the estimate of blood viscosity was more strongly associated with mortality in COVID-19 patients than other commonly used risk stratification measures.

This is a simple calculation that could be added to electronic medical records or lab forms to improve the chances of survival in COVID-19 patients who are hospitalised.

Researchers examined the records of 5,621 COVID-19 patients from six Mount Sinai Health System hospitals between February 27, 2020, and November 27, 2021. All had COVID 19 clinical and laboratory diagnoses were identified within 48 hours of hospitalisation and were followed until hospital discharge or death.

Hospitalised patients with high blood viscosity had a 60% higher death rate when measured under high flow conditions such as the arteries and a 32% higher mortality rate when measured under low flow conditions such as the microcirculation (blood circulation in the smallest vessels) than patients with low blood viscosity.

Acute phase reactants (fibrinogen, macroglobulins) that have been linked to acute COVID-19 infections raise blood viscosity. Blood viscosity is a combined measure of these acute phase reactants as well as the cellular components that can increase during infection.

When blood viscosity is high, physicians may consider therapeutic heparin, hydration, or glucocorticoid intensification to lessen the severity of the acute phase response to COVID-19.

"This study demonstrates the importance of determining blood viscosity in COVID-19 patients early in their hospitalisation, which is easily obtained through routine lab work." Dr Rosenson says the findings "can help determine the best treatment course for at-risk patients and help improve outcomes.

We are currently investigating the effects of therapeutic heparin to reduce the risk of complications during acute COVID-19 infections, which may greatly benefit those with high blood viscosity."