Which factor is most likely to affect blood viscosity?

Blood viscosity refers to the thickness and stickiness of blood, which is influenced primarily by the components that make up blood, with red blood cells (RBCs) playing a significant role. An increase in the RBC count leads to a higher viscosity because the greater number of cells increases the friction between them and impedes easy flow through the blood vessels. This is especially true in conditions such as polycythemia, where an excess number of red blood cells are present.

While temperature can influence viscosity slightly, it does not have the same direct impact as the RBC count. The other cellular components of blood, such as platelets and leukocytes, do contribute to the overall composition, but they have a much lesser effect on viscosity compared to the red blood cell count.

In summary, the RBC count is the most influential factor for blood viscosity due to its direct relationship with the cellular concentration of blood, significantly altering the flow properties under varying physiological conditions.