We hypothesized that moderate-altitude exposure results in an increase in RBCV and a decrease in PV, thereby necessitating reevaluation of the current sea-level-based Hb and HCT criteria used for diagnosing anemia and polycythemia for their utility in permanent altitude residents of Southern Saudi Arabia, a densely populated region situated at 2200 to 3000 m above sea level. The gene discussed is GSTM1; the disease is anemia (phenotype).