A cut-off value of hemoglobin (Hb) concentrations (<13.0 gm/dl in males, <12.0 gm/dl in females), mean cell volume (MCV) <80 fl and/or mean cell hemoglobin (MCH) <27 pg, and the results of the sickling test were used to categorize the participants into three groups: group I, normal (normal Hb, MCV, and MCH, and negative sickling test); group II, individuals with MCV < 80 fl and/or MCH < 27 pg, with or without anemia, and negative sickling test; group III, sickle positive (individuals with a positive sickling test, with or without anemia, regardless of MCV and/or MCH values). This evidence concerns the gene GSTM1 and anemia (phenotype).