Normal Hemoglobin Hemoglobin A2 HbA2 An adult hemoglobin component normally present in hemolysates from human erythrocytes in concentrations of about 3%. The hemoglobin is composed of two alpha chains and two delta chains. The percentage of HbA2 varies in some hematologic disorders, but is about double in beta-thalassemia. SCDO:1000364 alpha2delta2 Sufficient Normal Variant of Hemoglobin A Request inclusion into NCIT below "Hemoglobin"/"Normal Hemoglobin". MESH:D006443 A2, Hemoglobin