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paroxysmal nocturnal hemoglobinuria n.
An infrequent disorder the onset of which usually occurs in the third or fourth decades of life and is characterized by periods of hemolytic anemia, hemoglobinuria primarily at night, pallor, bronzing of the skin, moderate splenomegaly, and red blood cells that are macrocytic and vary considerably in size. Also called Marchiafava-Micheli syndrome.