What condition is characterized by an excess of red blood cells?

Polycythemia is characterized by an excess of red blood cells in the bloodstream, leading to increased blood viscosity and potential complications such as hypertension and clotting disorders. This condition can arise from various factors, including high altitude, where the body compensates for lower oxygen levels by producing more red blood cells, or it can be the result of a myeloproliferative disorder, where the bone marrow produces an abnormal number of red blood cells.

In contrast, leukemia refers to a cancer of the blood or bone marrow that leads to high numbers of white blood cells, rather than red blood cells. Anemia is a condition where there is a deficiency of red blood cells or hemoglobin, leading to reduced oxygen transportation in the body. Thrombocytopenia involves a low platelet count, affecting the blood's ability to clot, but does not pertain to red blood cells. Understanding these distinctions highlights why polycythemia is specifically recognized for excess red blood cell production.