Hemoglobin A2 may be elevated in a number of conditions.


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).


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