GSTM1 and Beta-thalassemia: RBC: red blood cells (million/ul), Hb: hemoglobin (g/dl), MCV: mean corpuscular volume (fl), MCH: mean corpuscular hemoglobin (pg), MCHC: mean corpuscular hemoglobin concentration (g/dl), RDW: red cell distribution width (%), IDA: iron deficiency anemia, BTT: beta-thalassemia trait