This patient also had elevated deoxyhemoglobin (HHb) not explained by methemoglobinemia alone; the low pulse oximetry (SpO<sub>2</sub>) reading suggested a rightward-shift oxyhemoglobin (O<sub>2</sub>Hb) dissociation curve, which is the opposite of that expected in methemoglobinemia. This evidence concerns the gene GSTM1 and methemoglobinemia.