An unexpected finding with pulse oximetry in a patient with hemoglobin Koln

THE hemoglobinopathies characterized by an unstable hemoglobin, an array of more than 100 similar disorders caused by mutations of the hemoglobin molecule, are inherited in an autosomal dominant pattern and produce hemoglobins that denature spontaneously. Clinically, these patients present with hemolytic anemia, which can be exacerbated by oxidants or infection. However, their clinical course usually is benign. An important feature of these disorders is variation in the affinity of the abnormal hemoglobin for oxygen. An unexpected finding during the care of a patient with hemoglobin Koln, one of the hemoglobinopathics characterized by an unstable hemoglobin, was artifactually low hemoglobin oxygen saturation (Sp(O₂)) recorded by pulse oximetry. It was hypothesized that methemoglobinemia produced by autoxidation of the unstable hemoglobin was responsible for the falsely decreased Sp(O₂) observed.