A novel hemoglobin, Bonn, causes falsely decreased oxygen saturation measurements in pulse oximetry

A 4-year-old boy and his father exhibited low oxygen saturation measured transcutaneously by pulse oximetry, a finding that could not be confirmed by arterial blood gas analysis. Both patients exhibited slight hemolysis in their blood, and the boy had a microcytic anemia. There was no evidence of hypoxemia or methemoglobinemia. Despite the normal results from the arterial blood gas analysis, a right-to-left-shunt was assumed in the boy until a cardiology examination excluded this diagnosis. Sleep apnea syndrome was suspected in the father and treated with nocturnal positive pressure respiration based on the low oxygen saturation values obtained with pulse oximetry. Only after consultation with our laboratory was a hemoglobin variant suspected and investigated.

We performed hemoglobin protein analysis by HPLC, electrophoretic separation, and spectrophotometry and DNA sequence analysis of the alpha-globin gene.

Both HPLC chromatographic separation and alkaline electrophoresis revealed a unique hemoglobin peak. In both patients, alpha-globin gene sequencing revealed a mutation resulting in a histidine-to-aspartatic acid substitution at position alpha87. The low oxygen saturation measurement by pulse oximetry was due to hemoglobin Bonn oxyhemoglobin having an absorption peak at 668 nm, near the 660 nm measured by pulse oximeters.

Hemoglobin Bonn is a novel hemoglobin variant of the proximal alpha-globin that results in falsely low oxygen saturation measurements with pulse oximetry.