MCV is a good index in screening thalassemia,[37] and in differentiation of thalassemia from iron deficiency anemia[38] or nonthalassemic microcytosis.[39] However, although decreased RBC count and low Hb concentration have the high power to diagnose iron-deficient anemia, the mature RBC has a life span of about 120 days, and it will take a long time for Hb and RBC indices to reflect the iron deficiency. The gene discussed is GSTM1; the disease is Iron deficiency anemia.