Hemoglobin A2 is comprised of 2 alpha and 2 delta globin chains. Hemoglobin A2 usually represents 1.5 to 3% of total hemoglobin.
Conditions associated with microcytosis (decreased MCV):
(1) beta-thalassemia
(2) sickle cell anemia with alpha thalassemia
(3) sickle cell anemia with beta-0 thalassemia
Conditions associated with macrocytosis: (elevated MCV):
(1) megaloblastic anemia
(2) zidovudine therapy for HIV
(3) congenital dyserythropoietic anemia (CDA) Type I
Conditions associated with normocytosis (normal MCV):
(1) normal person with normal hemoglobin
(2) hyperthyroidism
Most elevations in hemoglobin A2 are less than 10%. The highest levels (12%) can be seen in beta thalassemia. Levels higher than 12% should be investigated (see below).
The expected increase in hemoglobin A2 may be masked if there is a concurrent condition that decreases hemoglobin A2 (sse next section).
