The main reason for suspected thalassemia is low HbA2, but another possibility of this result is iron deficiency. And your child is short of iron. Serum iron is only one aspect, ferritin is only 20, which is abnormal. In addition, red blood cell distribution width also increased significantly, which is consistent with the performance of iron deficiency. So the diagnosis is iron deficiency anemia+-thalassemia. Therefore, it is necessary to supplement the iron for the child, and then check the blood routine after the iron index returns to normal. If HGB and MCH are still low, there is a great possibility of thalassemia, but hemoglobin should be significantly higher than the current level.
The absence of thalassemia in genetic examination does not mean that thalassemia does not exist. Because only the six most common pathogenic mutations were examined. If hemoglobin does not recover after several months of iron recovery, the child should be considered as a mild α thalassemia patient. Future spouses should thoroughly check whether they have thalassemia.