How Are Thalassemias Diagnosed?

Doctors diagnose thalassemias using blood tests, including a complete blood count (CBC) and special hemoglobin tests.

• A CBC provides information about the amount of hemoglobin and the different kinds of blood cells, such as red blood cells, in a sample of blood. People who have thalassemias have fewer healthy red blood cells and less hemoglobin in their blood than normal. People who have alpha or beta thalassemia trait may have smaller than normal red blood cells.
• Hemoglobin tests measure the types of hemoglobin in a blood sample. People who have thalassemias have problems with the alpha or beta globin protein chains of hemoglobin.

Moderate and severe thalassemias usually are diagnosed in early childhood. This is because signs and symptoms, including severe anemia, appear within the first 2 years of life.

People who have milder forms of thalassemia may be diagnosed after a routine blood test shows they have anemia. Doctors suspect thalassemia if a child has anemia and is a member of an ethnic group that's at increased risk for thalassemia. (See "Who Is At Risk for Thalassemias?")

Doctors also do tests on the amount of iron in the blood to find out whether the anemia is due to iron deficiency or thalassemia. Iron-deficiency anemia occurs when the body doesn't have enough iron to make hemoglobin. The anemia in thalassemia occurs because of a problem with either the alpha globin chain or the beta globin chain of hemoglobin, not because of a lack of iron.

Because thalassemias are passed on from parents to children, family genetic studies also can help diagnose the disorder. This involves taking a family medical history and doing blood tests on family members to show whether any have missing or altered hemoglobin genes.

If you know of family members who have thalassemias and you're thinking of having children, consider talking with your doctor and/or a genetic counselor. They can help determine your risk for passing on the disorder to a child.

If you're expecting a baby and you and your partner are thalassemia carriers, you may want to consider prenatal testing.

Prenatal testing involves taking a sample of amniotic fluid or tissue from the placenta. (Amniotic fluid is the fluid in the sac surrounding a growing embryo. The placenta is the organ that attaches the umbilical cord to the mother's womb.)  Tests done on the fluid or tissue can show whether your baby has thalassemia and how severe it's likely to be.