Hemoglobin Barts Normal adult hemoglobin is composed of two chains each of alpha and beta globin. Hb Barts (Hemoglobin Barts) is a tetramer with four gamma globin chains, and is essentially pathognomonic for one or another form of alpha thalassemia. Hb Barts has an extremely high affinity for oxygen, resulting in almost no oxygen delivery to the tissues. HP:0005507 UMLS:C3539063 Haemoglobin Barts Hb Barts Hb Bart is normally not present in adult blood. It makes up about 85-90 percent of hemoglobin in Hb Bart hydrops fetalis syndrome, and about 2-5 percent in HbH disease. Abnormal hemoglobin