Alpha Thalassemia Workup

Alpha thalassemia is frequently mistaken for iron deficiency anemia because both disorders have microcytic red blood cells. Iron therapy is not required for alpha thalassemia, and the procedures used to find a source of bleeding in patients with iron deficiency anemia have no value in patients with thalassemia. Measurements of serum iron and ferritin can provide laboratory evidence to exclude iron deficiency as the etiology for microcytosis.

Failure to exclude iron deficiency anemia in a patient with an alpha thalassemia syndrome may lead to continuation of supplemental iron therapy for an extended period, and the resulting iron overload may lead to secondary hemochromatosis. If iron overload continues longer than 1-2 years, it can lead to damage in multiple organs, including cardiac, hepatic, and endocrine dysfunction.

Workup relies primarily on laboratory evaluation, hemoglobin electrophoresis, and genetic testing. Bone marrow aspiration and biopsy are generally not helpful in diagnosing these conditions; they may be indicated if other confounding problems are noted.

Silent carrier

The following findings are noted in silent carriers (-α/αα):

• Hemoglobin level - Within the reference range
• Reticulocyte count - Normal
• Mean corpuscular volume (MCV) – 75-85 fL
• Mean corpuscular hemoglobin (MCH) - Around 26 pg

Alpha thalassemia trait

The following findings are noted in individuals with alpha thalassemia trait (-α/-α or --/αα):

• Hemoglobin level - Within the reference range
• Reticulocyte count - Normal
• MCV - 65-75 fL
• MCH - Around 22 pg

Hemoglobin H disease

Individuals with hemoglobin H (HbH) disease (-α/--) have moderate-to-severe anemia. The following findings are noted:

• Hemoglobin level - 7-10 g/dL
• Reticulocyte count - 5-10% (the higher the reticulocyte count, the more severe the hemolysis)
• MCV - 55-65 fL
• MCH - 20 pg
• Peripheral blood smear - Small misshapen red cells, hypochromia, microcytosis, and targeting
• Brilliant cresyl blue stain - HbH inclusion bodies

Hydrops fetalis (alpha thalassemia major)

Individuals with hydrops fetalis (--/--) have severe anemia. The following findings are noted:

• Hemoglobin - 4-10 g/dL
• MCV - 110-120 fL
• Peripheral blood smear - Severe anisopoikilocytosis, severe hypochromia, and nucleated red blood cells (RBCs)

Alpha thalassemia with sickle-cell anemia

Alpha thalassemia combined with sickle-cell anemia results in a higher hemoglobin concentration and improved RBC survival. The alpha-globin gene deletion is associated with improved RBC deformability, but the improved rheologic benefits often are overcome by the greater viscosity of a higher hematocrit. Clinically, this scenario is evidenced by a greater number of painful vaso-occlusive crises. It is noteworthy, however, that the incidence of stroke is lower than that seen in sickle-cell disease alone.

Although hemoglobin electrophoresis is not sensitive enough to diagnose alpha thalassemia syndromes, it can be very useful in quantitating and identifying different hemoglobin types.

Hemoglobin Bart’s is elevated at birth in patients with alpha thalassemia. In persons with HbH disease, 20-40% of total hemoglobin is hemoglobin Bart’s, along with typical findings of adult hemoglobin A, hemoglobin A2, and hemoglobin F. In silent carriers, however, the percentage is only 1-2%, with low or normal amounts of hemoglobin A2.^[15] In persons with alpha thalassemia trait, hemoglobin Bart’s accounts for about 5-15% of total hemoglobin.

The thalassemias were initially defined in terms of the ratio between the quantities of alpha-globin and beta-globin chains (α/β ratio). Altered α/β synthetic ratios occur in both alpha and beta thalassemias. The α/β ratios progressively decrease from silent carrier state to alpha thalassemia trait to HbH disease. Tests are performed by incubating red blood cells with radiolabeled amino acid and subsequently separating alpha- and beta-globin chains with urea carboxymethyl cellulose (CMC) chromatography.

In general, imaging studies are not useful in alpha thalassemia. However, because hepatosplenomegaly and gallstones are common in HbH disease, some imaging of these organs can be useful. Ultrasonography of the liver, gallbladder, and spleen frequently reveals gallstones, which consist of pigment resulting from hemolysis.

Hepatomegaly was seen in 70% of 502 patients in Thailand, 60% of 153 patients in Sardinia, and 14% of 88 patients in Taiwan. Splenomegaly is also common in HbH disease and was found in 79% of patients in Thailand, 60% in Sardinia, and 47% in Taiwan.

Genetic testing is currently available to establish the diagnosis and clarify the genetic abnormalities in patients with a family history or laboratory results suggestive of an alpha thalassemia syndrome.^[16] Polymerase chain reaction (PCR) and restriction endonuclease testing may be used. Recombinant DNA technology can be diagnostic, but is still considered research. Other genetic tests include gene mapping and anti-L globin monoclonal antibodies.

Genetic techniques can be helpful in some cases in which both the patient’s and the parents’ alpha-chain configurations are elucidated exactly, which can be useful in predicting the risk that a couple’s future offspring will be affected.

Peripheral blood smear may reveal target cells, microcytosis, hypochromia, and anisopoikilocytosis. Most silent carriers have only mild microcytosis, which can be differentiated from other common causes of microcytosis on the basis of serum iron and ferritin concentrations within the reference range.