MetHb Arterial

The MetHb Arterial test measures the fraction of your hemoglobin that is in the methemoglobin form using an arterial blood sample and co-oximetry. Methemoglobin is an oxidized form of hemoglobin that cannot carry oxygen effectively. When levels rise, oxygen delivery to tissues can be reduced even if there is enough hemoglobin present.

This test is usually performed as part of an arterial blood gas with co-oximetry when there is concern for a dyshemoglobinemia. It helps your care team confirm or rule out methemoglobinemia and guide treatment decisions.

Methemoglobinemia can cause symptoms such as headache, shortness of breath, fatigue, dizziness, and skin color changes. It may be triggered by certain medications, chemicals, or foods, and it can also be due to inherited conditions that affect how your red cells handle oxidant stress. Because standard pulse oximetry can be misleading in this situation, a co-oximetry measurement is important for accurate assessment.

Clinicians order this test when your symptoms and exposure history raise suspicion for a dyshemoglobinemia, or when oxygen readings and clinical appearance do not match. Identifying an elevated methemoglobin fraction helps target treatment, remove the trigger, and prevent complications.

Your clinician will interpret your result in the context of your symptoms, pulse oximetry, and exposures. A higher-than-expected fraction suggests methemoglobinemia and usually prompts a review of recent medications, products, and environmental exposures, along with decisions about supportive care or specific therapy. A result within the expected range generally rules out clinically significant methemoglobinemia at the time of testing.

If your level is elevated, your team may stop possible triggers and consider treatments that help your red cells return to normal function. People with glucose-6-phosphate dehydrogenase deficiency may need alternatives to standard therapy. Seek urgent care if you develop worsening shortness of breath, confusion, chest pain, or persistent color changes, even after testing, since additional evaluation may be needed.