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Immunology & Autoimmune
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Currently under review
Pending specialist review and validation.
Methemoglobin is a form of hemoglobin that cannot carry oxygen effectively. The MetHb Mixed test measures the proportion of your total hemoglobin that is in the methemoglobin form using co-oximetry on a mixed blood sample. This helps detect methemoglobinemia, a condition in which methemoglobin increases and reduces oxygen delivery to tissues.
This test is often performed when there is concern for exposure to certain medications or chemicals that can oxidize hemoglobin, or when an inherited enzyme or hemoglobin variant is suspected. It is done on whole blood and is part of a broader co-oximetry assessment that can also characterize other hemoglobin species.
Too much methemoglobin can lead to low oxygen delivery, causing symptoms such as gray or blue skin color, headache, shortness of breath, fatigue, or confusion. Clinicians order this test when they suspect acquired methemoglobinemia from drugs or chemicals, after use of topical anesthetics, during inhaled nitric oxide therapy, in certain critical care settings, or when a hereditary cause is considered.
Knowing your methemoglobin level helps your care team identify a trigger, stop harmful exposures, and decide on treatments. It can guide whether supportive care alone is enough or if specific therapy is needed, and it can help track improvement as the underlying cause is corrected.
Your clinician will interpret your result together with your symptoms, exam findings, pulse oximetry, and other co-oximetry measurements. A small amount of methemoglobin is expected in everyone. Higher values may suggest an acquired cause, such as a medication or chemical exposure, or less commonly a hereditary enzyme deficiency or hemoglobin variant.
If your level is elevated and you feel unwell, urgent medical care may be needed. Management often includes stopping the trigger, giving supplemental oxygen, and considering specific therapy based on your overall health, including conditions such as G6PD deficiency or anemia, and pregnancy status. Follow-up testing may be used to confirm improvement after treatment or after the exposure has been removed.
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.
Medications and agents such as benzocaine and other topical anesthetics, dapsone, nitrates or nitrites, phenazopyridine, and certain dyes can raise methemoglobin. Tell your clinician about all prescriptions, over-the-counter products, and exposures.
Therapies like inhaled nitric oxide and some extracorporeal circuits can increase methemoglobin formation. Levels may be monitored during treatment to guide dosing and safety.
Hemolysis, severe lipemia, icterus, or the presence of unusual dyes can affect spectrophotometric co-oximetry. Proper tube selection, prompt analysis, and avoiding contamination improve result accuracy.
Deficiency of cytochrome b5 reductase or hemoglobin M variants can cause lifelong elevations. Family history or persistently elevated results without clear exposure may prompt genetic evaluation.
Young infants have immature enzyme systems and may be more prone to methemoglobinemia, especially with certain medications or contaminated water sources. Clinicians interpret results in this context.
G6PD deficiency affects treatment choices and may complicate management. Underlying anemia or cardiorespiratory disease can worsen symptoms at a given methemoglobin level.
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