A full iron panel should be done. This includes serum ferritin, serum iron and TIBC or TSAT%. By looking at the results of these tests and also the results of a complete blood count (CBC), especially the RBC, which will be low if iron deficiency is present, but normally is a bit high for thal minors, you can get a pretty good idea of whether or not a thal minor has iron deficiency, as well. In my experience looking at blood reports of thal minors, ferritin is often low in minors and they do not have iron deficiency. I would say no minor should ever be prescribed iron based on a serum ferritin test, alone.