Anemia, defined as a concentration of hemoglobin (Hb) below the lower limit of the normal range for age (Table 1) [1], is a common issue in critically ill patients: Approximately two-thirds of critically ill adults are anemic at admission to the intensive care unit (ICU) [2, 3] and up to 98% of them have been reported to be anemic by ICU day 8 [4]. The gene discussed is GSTM1; the disease is anemia.