Sulfhemoglobin (SulfHb) is formed by
hemoglobin (Hb) oxidation by
sulfur compounds.
Sulfhemoglobinemia is mainly associated with drugs or intestinal bacterial overgrowth. Patients present with central
cyanosis, an abnormal pulse oximetry and normal arterial
oxygen partial pressure. These features are shared with
methemoglobinemia (MetHb) whose diagnosis requires an arterial co-oximetry. Depending on the device used, SulfHb may produce interference with this technique. We report two females aged 31 and 43 years, consulting at the emergency room with
cyanosis. Both had a history of acute and chronic, high dose
zopiclone ingestion. Pulse oximetry showed desaturation but with normal arterial
oxygen partial pressure. Cardiac and
pulmonary diseases were ruled out. Co-oximetry in two different analyzers showed interference or normal MetHb percentages. No other complications ensued, and
cyanosis decreased over days. Since MetHb was discarded among other causes of
cyanosis in a compatible clinical context, the diagnosis of
sulfhemoglobinemia was made. The confirmatory method is not available in Chile. The presence of SulfHb is difficult to diagnose, confirmatory tests are not readily available, and it frequently interferes with arterial co-oximetry. This is attributed to a similar absorbance peak of both pigments in arterial blood. Venous co-oximetry can be useful in this context. SulfHb is a self-limited condition in most cases, however it must be differentiated from
methemoglobinemia to avoid inappropriate treatments like
methylene blue.