Historically, isotope dilution methods has been considered the gold standard for the assessment of RCM (1); however, given the limited availability of this testing, hemoglobin (Hb) and hematocrit (Hct) values are commonly used as surrogate marker of RCM and completed replaced RCM calculation in the last edition of the WHO criteria for diagnosis of polycythemia vera (PV) (2). The gene discussed is GSTM1; the disease is acquired polycythemia vera.