The diagnosis of thalassemia may need to be considered in a patient with erythrocytic microcytosis, in unexplained hydrops fetalis, or for genetic counseling of patients at risk for thalassemia major. A panel of screening tests can help direct subsequent specialized testing.

Defective Production

Thalassemia Type

alpha globin


beta globin


delta and beta globins



Thalassemia may occur with:

(1) deletion of the entire globin gene (chromosome 16 for alpha gene, chromosome 11 for beta gene)

(2) small mutations within critical portions of the globin gene that prevent translation into protein

(3) hemoglobin variants (such as Hemoglobin Lepore) with defective production of abnormal globin chains


Abnormal tetramers in thalassemia:

(1) hemoglobin H: tetramer of 4 beta globin chains

(2) hemoglobin Barts: tetramer of 4 delta globin chains (hemoglobin F is composed of 2 alpha and 2 delta chains)


Screening panel for patients with microcytosis and possible thalassemia:

(1) serum ferritin level initially

Once any iron deficiency has been corrected, then perform

(2) quantitation of hemoglobins A2 and F

(3) hemoglobin electropheresis

(4) hemoglobin H inclusion body screen


Hemoglobin A2


1.5 – 3.5% of total hemoglobin

normal, or mixed iron deficiency and beta thalassemia

4.0 – 8.0%


> 10%

hemoglobin E, hemoglobin C, or hemoglobin O (co-elute with hemoglobin A2)


Hemoglobin electropheresis (alkaline pH, acid pH) can identify abnormal hemoglobins (E, Lepore, Constant Spring, H, etc.).


Hemoglobin H inclusion body screen:

(1) Examine the Wright stained blood smear to exclude intra-erythrocytic inclusions

(2) 6 drops of blood are mixed with 1 drop of supravital stain (brilliant cresyl blue, new methylene blue) and incubated at 37°C for exactly 1 hour

(3) Smears of sample examined for round, globular, peacock blue bodies within erythrocytes


Hemoglobin F

Hemoglobin H Inclusion Bodies


5.0 – 15%


delta-beta thalassemia trait

normal (0 - 2%)


hemoglobin H disease

normal (0 - 2%)

negative or occasional

alpha thalassemia trait


Confirmatory testing:

(1) alpha thalassemia trait: DNA genotype for alpha globin gene


Other conditions to consider once iron deficiency and thalassemia are excluded:

(1) anemia of chronic disease

(2) congenital sideroblastic anemia


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