What condition would most likely decrease blood viscosity?

Severe anemia is a condition characterized by a lower than normal number of red blood cells, which leads to a reduced concentration of hemoglobin in the blood. Since hemoglobin is a key component that contributes to blood viscosity, a decrease in red blood cell mass due to anemia directly results in a decrease in blood viscosity.

In this context, lower blood viscosity means the blood flows more easily through the vessels. This is particularly significant in clinical scenarios, as viscosity can influence overall cardiovascular function and flow dynamics. A decreased viscosity can help improve blood flow, especially in smaller vessels, allowing for better oxygen and nutrient delivery to tissues.

In contrast, conditions like severe dehydration would increase blood viscosity due to the reduction of plasma volume, while high hematocrit levels indicate an increased proportion of red blood cells, leading to increased viscosity. Elevated blood pressure, while it may relate to flow dynamics, does not directly decrease blood viscosity. Thus, severe anemia stands out as the condition most likely to cause a decrease in blood viscosity.