Complete blood count (CBC). The CBC is a snapshot of the cells and fluid in the bloodstream. Among other things, the CBC will tell the doctor how many red blood cells are present and how much hemoglobin is in them. It will give the doctor an evaluation of the size and shape of the red blood cells present, also called the red cell indices. These include the mean corpuscular volume (MCV), a measurement of the size of the red blood cells. A low MCV is often the first indication of thalassemia. If the MCV is low and iron-deficiency has been ruled out, thalassemia should be considered.
Blood smear (also called peripheral smear and manual differential). In this test, a trained laboratorian examines a thin layer of blood that is treated with a special stain, on a slide, under a microscope. The number and type of white blood cells, red blood cells, and platelets can be evaluated to see if they are normal and mature. A variety of disorders affect normal blood cell production. With thalassemia, the red blood cells are often microcytic (low MCV). Red cells may also:
- Be hypochromic
- Vary in size (anisocytosis) and shape (poikilocytosis)
- Be nucleated (normal, mature RBCs do not have a nucleus)
- Have uneven hemoglobin distribution (producing "target cells" that look like a bull's-eye under the microscope).
The greater the percentage of abnormal-looking red blood cells, the greater the likelihood of an underlying disorder and of impaired oxygen-carrying capability.
Iron studies. These may include: iron, ferritin, unsaturated iron binding capacity (UIBC), total iron binding capacity (TIBC), and percent saturation of transferrin. These tests measure different aspects of the body's iron storage and usage. They are ordered to help determine whether an iron deficiency is causing and/or exacerbating a person's anemia. One or more of them may also be ordered to help monitor the degree of iron overload in an individual with thalassemia.
Hemoglobinopathy (Hb) evaluation. This test measures the type and relative amounts of hemoglobin present in the red blood cells. Hemoglobin A, composed of both alpha and beta globin, is the normal type of hemoglobin found in adults. A greater percentage of Hb A2 and/or F is usually seen in beta thalassemia trait. Hb H may be seen in alpha thalassemia due to Hb H disease.
DNA analysis. This test is used to investigate deletions and mutations in the alpha and beta globin producing genes. Family studies can be done to evaluate carrier status and the types of mutations present in other family members. DNA testing is not routinely done but can be used to help diagnose thalassemia and to determine carrier status. Amniotic fluid is used in rare instances to person genetic testing of fetal DNA for thalassemia.