Blood Viscosity Defined

Vince · Apr 28, 2017

Blood viscosity is the thickness and stickiness of blood. It is a direct measure of the ability of blood to flow through the vessels. It is also a key screening test that measures how much friction the blood causes against the vessels, how hard the heart has to work to pump blood, and how much oxygen is delivered to organs and tissues. Importantly, high blood viscosity is easily modifiable with safe lifestyle-based interventions.
Blood Viscosity Basics

MargaretLopez · May 17, 2017

I agree with your post. Thanks for the awareness.

Nelson Vergel · Feb 24, 2025

Sustained hyperviscosity, often caused by elevated hematocrit or plasma viscosity, has significant long-term effects on cardiovascular health. Below are the key findings:

Long-Term Cardiovascular Effects of Sustained Hyperviscosity

Increased Risk of Coronary Heart Disease (CHD):
- Elevated plasma viscosity is independently associated with a higher risk of coronary heart disease (CHD). Studies show that individuals with higher plasma viscosity levels have an increased likelihood of experiencing major CHD events such as myocardial infarction and cardiac death. For example, men in the highest quintile of plasma viscosity had a 3.31-fold higher risk of CHD compared to those in the lowest quintile, even after adjusting for conventional risk factors like cholesterol and blood pressure1.
Atherosclerosis Development:
- Sustained hyperviscosity contributes to the development of atherosclerosis by increasing endothelial shear stress and promoting vascular inflammation. This process facilitates the formation of atheromas, particularly in areas of disturbed blood flow, such as arterial bifurcations. Increased blood viscosity also promotes low-density lipoprotein (LDL) accumulation in these regions, further predisposing individuals to thrombosis and ischemic events2.
Thrombotic Events:
- Hyperviscosity increases the risk of thrombotic complications, including cerebrovascular accidents (strokes) and myocardial infarctions. Thrombosis is exacerbated by microvascular stasis caused by high blood viscosity, which impairs tissue perfusion and oxygen delivery. This can result in severe outcomes like transient ischemic attacks (TIAs) or long-term neurological deficits3.
Microvascular Impairment:
- Sustained hyperviscosity reduces blood flow in microcirculation due to increased resistance, leading to impaired tissue perfusion. This can cause symptoms such as fatigue, muscle weakness, and paresthesia. Over time, chronic microvascular stasis may contribute to organ dysfunction and ischemia3.
Hypertension and Left Ventricular Hypertrophy:
- Hyperviscosity elevates systemic vascular resistance, contributing to hypertension. Chronic hypertension combined with high blood viscosity can lead to left ventricular hypertrophy (LVH), a condition that increases the risk of heart failure and arrhythmias2.
Stroke Risk:
- Studies indicate that increased blood viscosity and hematocrit levels are significant predictors of stroke risk. Even after adjusting for other factors like smoking and LDL cholesterol levels, hyperviscosity remains independently associated with ischemic stroke2 3.
Complications in Specific Conditions:
- In conditions like cyanotic congenital heart disease (CCHD), chronic hypoxia-induced erythrocytosis leads to severe hyperviscosity. This not only impairs oxygen delivery but also increases the likelihood of thrombotic events and organ damage due to reduced perfusion3.

Clinical Implications

Sustained hyperviscosity is a critical factor in cardiovascular morbidity and mortality. Monitoring and managing hematocrit and plasma viscosity levels are essential for reducing risks associated with CHD, stroke, and other vascular complications. Interventions such as therapeutic phlebotomy or addressing underlying causes like erythrocytosis may help mitigate these risks in affected individuals3.