Final answer:
Polycythemia vera is a bone marrow disease that causes an elevated RBC count. It can increase blood viscosity and blood pressure, and is more common in males and elderly patients.
Step-by-step explanation:
Polycythemia vera (PV) is a type of bone marrow disease that causes the excessive production of immature erythrocytes, resulting in an elevated RBC count. This condition can be detected through an elevated hematocrit, which is the percentage of red blood cells in the blood. PV can dangerously increase the viscosity of blood, raising blood pressure and making it more difficult for the heart to pump blood throughout the body. It is a relatively rare disease that occurs more often in males than females and is more likely to be present in elderly patients over the age of 60.