What is the role of lab tests in the workup of beta thalassemia?

Updated: Dec 19, 2018
  • Author: Pooja Advani, MD; Chief Editor: Emmanuel C Besa, MD  more...
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Answer

The diagnosis of beta thalassemia minor usually is suggested by the presence of the following:

  • Mild, isolated microcytic anemia

  • Target cells on the peripheral blood smear (see the images below)

  • A normal red blood cell (RBC) count

    Peripheral smear in beta-zero thalassemia minor sh Peripheral smear in beta-zero thalassemia minor showing microcytes (M), target cells (T), and poikilocytes.
    Peripheral smear from a patient with beta-zero tha Peripheral smear from a patient with beta-zero thalassemia major showing more marked microcytosis (M) and anisopoikilocytosis (P) than in thalassemia minor. Target cells (T) and hypochromia are prominent.

Heinz bodies, which represent inclusions within RBCs consisting of denatured hemoglobin (Hb), may also be seen in the peripheral blood. [11]

Elevation of the Hb A2 level, demonstrated by electrophoresis or column chromatography, confirms the diagnosis of beta thalassemia trait. The Hb A2 level in these patients usually is approximately 4-6%. In rare cases of concurrent severe iron deficiency, an increased Hb A2 level may not be observed, although it becomes evident with iron repletion. The increased Hb A2 level also is not observed in patients with the rare delta-beta thalassemia trait. An elevated Hb F level is not specific to patients with the beta thalassemia trait.

Free erythrocyte porphyrin (FEP) tests may be useful in situations in which the diagnosis of beta thalassemia minor is unclear. The FEP level is normal in patients with the beta thalassemia trait, but it is elevated in patients with iron deficiency or lead poisoning.

Alpha thalassemia is characterized by genetic defects in the alpha-globin gene, and this variant has features similar to beta thalassemia (see Diagnostic Considerations). Patients with this disorder have normal Hb A2 levels. Establishing the diagnosis of the alpha thalassemia trait requires measuring either the alpha-beta chain synthesis ratio or performing genetic tests of the alpha-globin cluster (using Southern blot or polymerase chain reaction [PCR] assay tests).

Iron studies (iron, transferrin, ferritin) are useful in excluding iron deficiency and the anemia of chronic disorders as the cause of the patient's anemia.

Evidence of hemolysis in the form of indirect hyperbilirubinemia, low haptoglobin, and elevated lactate dehydrogenase may be seen as a result of ineffective erythropoiesis and consequent destruction of these RBCs.

Patients may require a bone marrow examination to exclude certain other causes of microcytic anemia. Physicians must perform an iron stain (Prussian blue stain) to diagnose sideroblastic anemia (ringed sideroblasts).

The Mentzer index is defined as mean corpuscular volume per red blood cell count. An index of less than 13 suggests that the patient has the thalassemia trait, and an index of more than 13 suggests that the patient has iron deficiency. [8]


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