Hemoglobin A3 is a predominantly historic term for a fraction of normal hemoglobin molecules that is seen when hemoglobin is separated out using starch block electrophoresis. These Hemoglobin molecules are non-enzymatic modifications of the hemoglobin molecules and they encompass hemoglobinA1c, Hb1a (both the subtypes Hb1a1 and Hb1a2) and Hb1b.[1]
As these Hemoglobin subtypes are formed over time, they are found more prevalent in older red cells.