noun
polycythemia; erythrocytosis
Medical term for an abnormal increase in red blood cells. The spelling 赤血球増加症 is standard; alternative English spellings include polycythaemia and hypercythemia.
赤血球増加症は、血液中の赤血球が過剰になる状態です。
Polycythemia is a condition in which there are too many red blood cells in the blood.
Compound of 赤血球 (red blood cell) + 増加 (increase) + 症 (disease/condition).