Platform
Company
Immunology & Autoimmune
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Currently under review
Pending specialist review and validation.
This test measures methemoglobin in a sample of venous blood. Methemoglobin is a form of hemoglobin that has been oxidized and cannot effectively carry oxygen to your tissues. Laboratories detect it using a co-oximeter, which separates and quantifies different hemoglobin species in whole blood.
Your result is reported as the fraction of total hemoglobin present as methemoglobin. Small amounts can be present normally. Higher levels may occur after exposure to certain medicines or chemicals, or in rare inherited conditions that affect how red blood cells keep hemoglobin in its usual oxygen-carrying form.
Clinicians order this test when there are signs that blood is not carrying oxygen well, such as unexplained blue skin color that does not improve with oxygen, shortness of breath, headache, dizziness, or fatigue. It is also used if you have been exposed to oxidizing drugs or chemicals, including some antibiotics, local anesthetics, and nitrates, or if an infant has symptoms after formula or water exposures.
Results help confirm methemoglobinemia and guide treatment decisions, such as stopping the offending agent, giving supportive care, and considering antidotal therapy when appropriate. The test can also help monitor your response to treatment and evaluate for rare inherited forms that may cause recurrent symptoms.
Very low methemoglobin levels are expected in healthy people. If your result is higher, your care team will look for causes such as recent medications, topical anesthetics, inhaled or ingested chemicals, or an underlying enzyme or hemoglobin variant. Management typically focuses on removing the trigger, providing oxygen, and using specific therapy if needed.
If your level is elevated and you feel unwell, seek medical care promptly. Tell your clinician about all prescription and over-the-counter medicines, supplements, and recent exposures. People with certain conditions, such as glucose-6-phosphate dehydrogenase deficiency or pregnancy, may need tailored treatment choices. Your clinician may repeat the test to track improvement as the exposure clears or therapy takes effect.
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 prilocaine sprays and gels, nitrates or nitrites, phenazopyridine, and some antimalarials can raise methemoglobin. Industrial exposures to aniline dyes or nitrites can do the same. Tell your clinician about all recent exposures.
Infants are more susceptible because their red cells have lower enzyme activity and more fetal hemoglobin. Formula prepared with nitrate-contaminated well water or certain diarrhea illnesses can increase risk.
Rare enzyme deficiencies, such as cytochrome b5 reductase deficiency, or hemoglobin M variants can cause persistent or recurrent elevations. Family history and genetic testing may be considered if elevations recur without clear triggers.
Methemoglobin is measured best on fresh, heparinized whole blood analyzed promptly. Delays, excessive air exposure, or improper storage can affect co-oximetry results. Inform the lab if specimen transport was prolonged.
Preexisting lung or cardiac conditions can worsen symptoms at a given methemoglobin level. Clinicians interpret results together with your oxygen saturation, symptoms, and overall health.
If you have glucose-6-phosphate dehydrogenase deficiency, certain treatments may be avoided or used with caution. Your care team may choose alternative therapies and monitor closely.
References