CD235a (Glycophorins A, GPA) is a single pass membrane sialoglycoprotein expressed in mature erythrocytes and erythroid precursor cells. CD235a is the carrier of blood group M and N specificities. CD235a provides cells with a large mucin-like that may serve as a barrier to cell fusion, minimizing aggregation between red blood cells in the circulation. CD235a is useful to characterize erythroid cell development and aid in the diagnosis of erythroid leukemia.