A compound formed by the combination of hemoglobin and oxygen. It is a complex in which the oxygen is bound directly to the iron without causing a change from the ferrous to the ferric state.

An increase in circulating RETICULOCYTES, which is among the simplest and most reliable signs of accelerated ERYTHROCYTE production. Reticulocytosis occurs during active BLOOD regeneration (stimulation of red bone marrow) and in certain types of ANEMIA, particularly CONGENITAL HEMOLYTIC ANEMIA.