Final answer:
Excess RBCs lead to polycythemia, a condition with increased blood viscosity due to elevated RBC counts, which can be caused by both physiological adaptations and pathological conditions such as polycythemia vera.
Step-by-step explanation:
Excess red blood cells (RBCs) in the body leads to a condition known as polycythemia. This is not to be confused with pernicious anemia, which is a decrease in RBCs due to a vitamin B12 deficiency. In contrast, polycythemia is characterized by an elevated number of RBCs and can arise for various reasons, including living at high altitudes where there is lower oxygen saturation in the air, leading to a compensatory increase in RBC production to better transport oxygen throughout the body. However, there are pathological forms of polycythemia, such as polycythemia vera, a bone marrow disease that results in the excessive production of immature erythrocytes, which can increase blood viscosity. This increased viscosity can lead to complications such as higher blood pressure and an increased workload on the heart.