There are several lab tests may be used to help detect and diagnose thalassemia:
Complete blood count (CBC).
CBC determines the number of red blood cells present and how much hemoglobin is in them. It evaluates the size and shape of the red blood cells present, reported as 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 as a cause, thalassemia should be considered.
Blood smear (also called peripheral smear and manual differential).
In this test, the number and type of white blood cells, red blood cells, and platelets are evaluated to see if they are normal and mature. With thalassemia, the red blood cells often appear smaller than normal (microcytic, low MCV). Red cells may also:
- Be paler than normal (hypochromic)
- Vary in size and shape (anisocytosis and 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)
These may include: iron, ferritin, UIBC, TIBC, and percent saturation of transferrin. These tests measure different aspects of the body's iron storage and usage. The tests are ordered to help determine whether an iron deficiency is the cause of a person's anemia.
- Alpha thalassemia is sometimes confused with iron deficiency anemia because both disorders have smaller than usual (microcytic) red blood cells. If someone has thalassemia, his or her iron levels are not expected to be low. Iron therapy will not help people with alpha thalassemia and may lead to iron overload, which can cause organ damage over time.
- Erythrocyte porphyrin tests may be used to distinguish an unclear beta thalassemia minor diagnosis from iron deficiency or lead poisoning. Individuals with beta thalassemia will have normal porphyrin levels, but those with the latter conditions will have elevated porphyrin.
Hemoglobinopathy (Hb) evaluation (hemoglobin electrophoresis).
This test assess the type and relative amounts of hemoglobin present in red blood cells.
- Hemoglobin A (Hb A), normally makes up 95% to 98% of hemoglobin in adults.
- Hemoglobin A2 (HbA2) is usually 2% to 3% of hemoglobin in adults.
- Hemoglobin F usually makes up less than 2%.
Beta thalassemia upsets the balance of beta and alpha hemoglobin chain formation and causes an increase in those minor hemoglobin components. So individuals with the beta thalassemia major usually have larger percentages of Hb F. Those with beta thalassemia minor usually have elevated fraction of Hb A2. Hb H is a less common form of hemoglobin that may be seen in some cases of alpha thalassemia. Hb S is the hemoglobin more common in people with sickle cell disease.
DNA analysis. These tests are used to help confirm mutations in the alpha and beta globin-producing genes. DNA testing is not routinely done but can be used to help diagnose thalassemia and to determine carrier status, if indicated.