Point-of-care pulse oximetry in patients with methemoglobinemia is therefore not accurate because methemoglobin absorbs both infrared and red light equally, which interferes with the measured percentage of oxyHb and deoxyHb (Hb oxygen saturation SO2 of ~86% in our affected cat measured at the time of anesthesia induction). This evidence concerns the gene GSTM1 and methemoglobinemia.