In diagnosing thalassemias, a physician will perform a physical examination and compile a medical history. A family history of thalassemia can be a strong indicator that the patient may have this condition. Genetic testing of family members also can help indicate if a family history of thalassemia is present.  

Prenatal testing can help determine if a fetus has thalassemia, and how severe the condition is likely to be. A blood test called hemoglobin electrophoresis can be performed on newborn infants to check for thalassemia or thalassemia trait. This test, in part, looks for certain types of abnormal hemoglobin in the blood, specifically hemoglobin D or hemoglobin H.

A physician will rule out other conditions before diagnosing alpha thalassemia. For example, the fatigue associated with alpha thalassemia is similar to that caused by an iron deficiency. Blood tests can reveal the amount of iron in a person’s blood, which can help a physician distinguish between a diagnosis of iron deficiency and alpha thalassemia.

A complete blood count (CBC) also can provide valuable insights into whether or not a patient has thalassemia. Normal amounts of hemoglobin in adults range from 12 grams to 18 grams per deciliter of blood. CBC results that detect less hemoglobin than normal, fewer red blood cells than normal and smaller red blood cells than normal may indicate thalassemia.