Platform
Company
Electrolytes
Review status
Currently under review
Pending specialist review and validation.
Methemoglobin is a form of hemoglobin that has been oxidized and cannot carry oxygen effectively. The MetHb test measures the proportion of your hemoglobin that is in this oxidized state using co-oximetry, a method that analyzes how light passes through a blood sample to identify different hemoglobin species.
Your sample is drawn from a vein or an artery, depending on your clinical situation, and processed promptly to reflect your current oxygen-carrying status. This measurement is often performed alongside other co-oximetry values, such as oxyhemoglobin and carboxyhemoglobin, to give a fuller picture of blood oxygen transport.
When methemoglobin is elevated, oxygen delivery to tissues is reduced, which can lead to bluish skin or lips, headache, dizziness, shortness of breath, fatigue, and in more serious cases confusion. Clinicians order this test when your symptoms or monitor readings suggest a problem with oxygenation that does not fit typical lung or heart causes.
The test is especially helpful if you may have been exposed to medicines or chemicals known to oxidize hemoglobin, including certain antibiotics, local anesthetics, nitrates, nitrites, or industrial compounds. It is also relevant in young infants, in people with inherited red cell enzyme defects, and in those with chronic heart or lung conditions who may be more vulnerable to reduced oxygen delivery.
Your clinician will interpret the result in the context of your symptoms, possible exposures, vital signs, and other lab tests. If your value is higher than expected, the first steps usually include stopping a triggering drug or chemical and treating any symptoms. Some people benefit from specific therapies such as methylene blue or vitamin C, while others can be managed with observation and supportive oxygen.
If your result is within the expected range, it suggests methemoglobinemia is unlikely to be the cause of your symptoms. If elevated results persist without an obvious exposure, your care team may consider inherited causes and may recommend additional testing. Discuss your result and next steps with your clinician, including whether any household members could be at similar risk from shared exposures.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Drugs such as dapsone, benzocaine or lidocaine sprays, nitrates or nitrites, and certain antibiotics or herbicides can increase methemoglobin. Tell your clinician about all prescriptions, over-the-counter products, and recent exposures.
Strongly colored substances in blood, such as dyes, severe jaundice, or marked lipemia, can interfere with co-oximetry. Prompt analysis and proper instrument calibration help ensure accurate results.
Therapies for suspected methemoglobinemia, including methylene blue or high dose vitamin C, can lower the measured value. If treatment started before blood was drawn, the result may underestimate the peak level.
Young infants and people with hereditary red cell enzyme deficiencies are more susceptible to elevated methemoglobin. In individuals with G6PD deficiency, some treatments may be unsafe or less effective.
Levels can change over hours as the body reduces methemoglobin or as exposure continues. Testing too early or too late can miss the peak, so let your clinician know when symptoms and exposures began.
Red blood cell transfusion can dilute or alter methemoglobin levels. Significant blood loss or transfusion history should be shared with the laboratory and your clinician when interpreting results.
References