Thalassemia is a genetic disease, a hereditary condition, caused by abnormal production of globin in hemoglobin, leading to hemolytic anemia. Patients with thalassemia should first undergo a routine blood test. If the routine blood test indicates anemia or even if there is no anemia but the red blood cells are very small, it suggests a high possibility of thalassemia. At this point, further screening for thalassemia genes should be conducted to confirm the diagnosis. Once thalassemia is definitively diagnosed, it can be classified as mild, moderate, or severe based on the genotype.