Final answer:
Polycythemia is the condition characterized by an abnormal increase in the number of red blood cells, which can lead to higher blood viscosity and potential complications.
Step-by-step explanation:
Polycythemia is defined as a condition where there is an abnormal increase in the number of red blood cells (RBCs) in the blood. This increase can lead to a higher hematocrit level, which is the ratio of the volume of red cells to the volume of whole blood. Polycythemia can be a temporary condition caused by factors such as dehydration, where the plasma volume decreases and the concentration of red blood cells appears higher. However, there can also be continual forms of polycythemia, such as those experienced by individuals living at high altitudes, where it serves as a compensatory mechanism for lower atmospheric oxygen levels. A more serious form of polycythemia, known as polycythemia vera, results from a disease of the bone marrow, leading to the production of excessive amounts of immature erythrocytes. This disease can increase blood viscosity, making it hard for the heart to pump blood and potentially raising blood pressure.