| Methods that are useful for detecting methemoglobinemia | |
| Blood gas measurement (arterial or venous) | The vast majority of blood gas analyzers in the US will detect methemoglobin. If methemoglobinemia is suspected and a level is not reported, speak with laboratory personnel to determine if the information is available. |
| Co-oximetry | Specialized pulse oximeter that uses multiple wavelengths of light and can detect absorption of methemoglobin at 630 nm. |
| Evelyn-Malloy assay | Assay in which addition of cyanide eliminates absorption peak of methemoglobin. Considered to be the most accurate but rarely available in a timely fashion to guide patient care. |
| Methods that CANNOT be used to detect methemoglobinemia | |
| Routine pulse oximetry | Unable to distinguish between methemoglobin and normal oxy- and deoxy-hemoglobin. High levels of methemoglobin typically result in an SaO2 reading of approximately 85% that does not increase with supplemental oxygen. |
| PaO2 and SaO2 readings on blood gases | These may be normal or falsely elevated despite severe methemoglobinemia. |
