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Methemoglobinemia Workup

  • Author: Mary Denshaw-Burke, MD, FACP; Chief Editor: Emmanuel C Besa, MD  more...
Updated: Jan 04, 2016

Laboratory Studies

Investigations to rule out hemolysis (complete blood count [CBC], reticulocyte count, peripheral smear review, lactate dehydrogenase [LDH], bilirubin, haptoglobin and Heinz body preparation) and end-organ dysfunction or failure (liver function tests, electrolytes, renal function tests) should be included in the workup. Urine pregnancy tests should be performed in females of childbearing age.

Investigations to evaluate a hereditary cause for methemoglobinemia should be ordered when appropriate. Hemoglobin electrophoresis and DNA sequencing of the globin chain gene can be used to identify hemoglobin M.

Specific enzyme assays (nicotinamide adenine dinucleotide [NADH]–dependent reductase, cytochrome b5 reductase) may be determined, often in multiple cell lines (ie, platelets, granulocytes, and fibroblasts), to diagnose inherited cases. A quick and easy bedside test for determining whether dark blood is due to methemoglobinemia is to bubble 100% oxygen in a tube that contains the dark blood. Blood that remains dark likely does so because of the presence of methemoglobin.

Another simple test (and one that is less likely to splash potentially infectious blood) is to place 1-2 drops of blood on white filter paper, then evaluate for color change upon exposure to oxygen. (This test can be accelerated by gently blowing supplemental oxygen onto the filter paper.) Deoxygenated hemoglobin changes from dark red or violet to bright red, whereas methemoglobin remains brown.

Serum levels of nitrites or other offending drugs may be determined. Often, these results are not immediately available, and treatment may have to be started empirically if the index of suspicion is high.


Arterial Blood Gas Determination

The presence of methemoglobin can falsely elevate the calculated oxygen saturation when arterial blood gases (ABGs) are obtained. One possible clue to the diagnosis of methemoglobinemia is the presence of a “saturation gap.” This occurs when there is a difference between the oxygen saturation measured on pulse oximetry and the oxygen saturation calculated on the basis of ABG results.

The partial pressure of oxygen (PO2) value of the ABG measurement reflects plasma oxygen content and does not correspond to the oxygen-carrying capacity of hemoglobin. It should be within the reference range in patients with methemoglobinemia.




Co-oximetry should be performed if available. The co-oximeter is an accurate device for measuring methemoglobin and is the key to diagnosing methemoglobinemia. It is a simplified spectrophotometer that can measure the relative absorbance of 4 different wavelengths of light and thus is capable of differentiating methemoglobin from carboxyhemoglobin, oxyhemoglobin, and deoxyhemoglobin. Newer co-oximeters can also measure sulfhemoglobin, which can be confused with methemoglobin by older devices.

Availability of appropriate equipment may be a problem. Lipemic specimens may result in a falsely elevated methemoglobin level. In addition, the presence of methylene blue interferes with the accurate measurement of methemoglobin by co-oximetry, hence this method cannot be used to monitor methemoglobin levels after treatment with methylene blue is initiated. Blood substitutes can cause co-oximetry to yield unreliable results.

Pulse oximetry

Pulse oximetry is used extensively in the evaluation of patients with cyanosis and respiratory distress. Findings of bedside pulse oximetry in the presence of methemoglobinemia may be misleading. Pulse oximetry measurements with low-levels of methemoglobinemia often result in falsely low values for oxygen saturation and are often falsely high in those with high-level methemoglobinemia. The reason for these inaccuracies is as follows.

The pulse oximeter only measures the relative absorbance of 2 wavelengths of light (660 nm and 940 nm) to differentiate oxyhemoglobin from deoxyhemoglobin. The ratio of absorption of light at each of these wavelengths is converted into oxygen saturation by using calibration curves. Methemoglobin increases absorption of light at both wavelengths (more at 940 nm) and therefore offers optical interference to pulse oximetry by falsely absorbing light.

As a result, oxygen saturations by pulse oximetry in methemoglobinemia plateau at about 85%; therefore, a patient with a methemoglobin level of 5% and a patient with a level of 40% have approximately the same saturation values on pulse oximetry (~85%). The severity of the cyanosis does not correspond to the pulse oximetry reading: a patient may appear extremely cyanotic but still have a pulse oximetry reading in the high 80s.

However, newer multiwavelength pulse oximeters have been developed that can detect methemoglobinemia with an accuracy comparable to that achievable with co-oximeters.


Other Studies

Potassium cyanide test

This test can distinguish between methemoglobin and sulfhemoglobin. Methemoglobin reacts with cyanide to form cyanomethemoglobin, which has a bright red color. Sulfhemoglobin does not react with cyanide and therefore does not change to a bright red color.

Diagnostic imaging

Imaging studies of the chest and echocardiography may be helpful to exclude pulmonary or cardiac disease.

Contributor Information and Disclosures

Mary Denshaw-Burke, MD, FACP Clinical Assistant Professor of Medicine, Jefferson Medical College of Thomas Jefferson University; Clinical Assistant Professor, Affiliated Clinical Faculty of the Lankenau Institute for Medical Research; Program Director of Hematology/Oncology Fellowship, Education Coordinator for Oncology, Lankenau Medical Center

Mary Denshaw-Burke, MD, FACP is a member of the following medical societies: American College of Physicians

Disclosure: Nothing to disclose.


Mudra Kumar, MD, MRCP, FAAP Professor of Pediatrics, Course Director, Course 6 MSII, Preclerkship Director, Clinical Integration, Department of Pediatrics, University of South Florida Morsani College of Medicine

Mudra Kumar, MD, MRCP, FAAP is a member of the following medical societies: American Academy of Pediatrics, American Society of Hematology, American Society of Pediatric Hematology/Oncology

Disclosure: Nothing to disclose.

Deric C Savior, MD Fellow, Department of Hematology/Oncology, Lankenau Hospital

Disclosure: Nothing to disclose.

Amy Lawser Curran, MD Fellow, Department of Hematology/Oncology, Lankenau Hospital

Amy Lawser Curran, MD is a member of the following medical societies: Alpha Omega Alpha, Sigma Xi

Disclosure: Nothing to disclose.

Elizabeth DelGiacco, DO Chief Fellow, Department of Hematology/Oncology, Main Line Health, Lankenau Medical Center

Elizabeth DelGiacco, DO is a member of the following medical societies: American Society of Hematology, American Society of Clinical Oncology

Disclosure: Nothing to disclose.

Chief Editor

Emmanuel C Besa, MD Professor Emeritus, Department of Medicine, Division of Hematologic Malignancies and Hematopoietic Stem Cell Transplantation, Kimmel Cancer Center, Jefferson Medical College of Thomas Jefferson University

Emmanuel C Besa, MD is a member of the following medical societies: American Association for Cancer Education, American Society of Clinical Oncology, American College of Clinical Pharmacology, American Federation for Medical Research, American Society of Hematology, New York Academy of Sciences

Disclosure: Nothing to disclose.


Steven K Bergstrom, MD Department of Pediatrics, Division of Hematology-Oncology, Kaiser Permanente Medical Center of Oakland

Steven K Bergstrom, MD is a member of the following medical societies: Alpha Omega Alpha, American Society of Clinical Oncology, American Society of Hematology, American Society of Pediatric Hematology/Oncology, Children's Oncology Group, and International Society for Experimental Hematology

Disclosure: Nothing to disclose.

Matthew Bouchard, MD Consulting Staff, Department of Emergency Medicine, Altoona Regional Health System

Disclosure: Nothing to disclose.

Michael J Burns, MD Instructor, Department of Emergency Medicine, Harvard University Medical School, Beth Israel Deaconess Medical Center

Michael J Burns, MD is a member of the following medical societies: American Academy of Clinical Toxicology, American College of Emergency Physicians, American College of Medical Toxicology, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Marcel E Conrad, MD Distinguished Professor of Medicine (Retired), University of South Alabama College of Medicine

Marcel E Conrad, MD is a member of the following medical societies: Alpha Omega Alpha, American Association for the Advancement of Science, American Association of Blood Banks, American Chemical Society, American College of Physicians, American Physiological Society, American Society for Clinical Investigation, American Society of Hematology, Association of American Physicians, Association of Military Surgeons of the US, International Society of Hematology, Society for Experimental Biology and Medicine, and Southwest Oncology Group

Disclosure: Nothing to disclose.

Max J Coppes, MD, PhD, MBA Senior Vice President, Center for Cancer and Blood Disorders, Children's National Medical Center; Professor of Medicine, Oncology, and Pediatrics, Georgetown University School of Medicine; Clinical Professor of Pediatrics, George Washington University School of Medicine and Health Sciences

Max J Coppes, MD, PhD, MBA is a member of the following medical societies: American Association for Cancer Research, American Society of Pediatric Hematology/Oncology, and Society for Pediatric Research

Disclosure: Nothing to disclose.

Kathy L Ferguson, DO Attending Physician, Department of Emergency Medicine, New York Hospital of Queens

Kathy L Ferguson, DO is a member of the following medical societies: American College of Emergency Physicians and American College of Medical Toxicology

Disclosure: Nothing to disclose.

Lance W Kreplick, MD, FAAEM, MMM Medical Director of Hyperbaric Medicine, Fawcett Wound Management and Hyperbaric Medicine; Consulting Staff in Occupational Health and Rehabilitation, Company Care Occupational Health Services; President and Chief Executive Officer, QED Medical Solutions, LLC

Lance W Kreplick, MD, FAAEM, MMM, is a member of the following medical societies: American Academy of Emergency Medicine and American College of Physician Executives

Disclosure: Nothing to disclose.

David C Lee, MD Research Director, Department of Emergency Medicine, Associate Professor, North Shore University Hospital and New York University Medical School

David C Lee, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Medical Toxicology, and Society for Academic Emergency Medicine

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Sharada A Sarnaik, MBBS Professor of Pediatrics, Wayne State University School of Medicine; Director, Sickle Cell Center, Attending Hematologist/Oncologist, Children's Hospital of Michigan

Sharada A Sarnaik, MBBS is a member of the following medical societies: American Association of Blood Banks, American Association of University Professors, American Society of Hematology, American Society of Pediatric Hematology/Oncology, New York Academy of Sciences, and Society for Pediatric Research

Disclosure: Nothing to disclose.

Paul Schick, MD Emeritus Professor, Department of Internal Medicine, Jefferson Medical College of Thomas Jefferson University; Research Professor, Department of Internal Medicine, Drexel University College of Medicine; Adjunct Professor of Medicine, Lankenau Hospital

Paul Schick, MD is a member of the following medical societies: American College of Physicians and American Society of Hematology

Disclosure: Nothing to disclose.

John Schoffstall, MD Associate Professor, Department of Emergency Medicine, Medical College of Pennsylvania

John Schoffstall, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, Pennsylvania Medical Society, and Society for Academic Emergency Medicine

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Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

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Asim Tarabar, MD Assistant Professor, Director, Medical Toxicology, Department of Emergency Medicine, Yale University School of Medicine; Consulting Staff, Department of Emergency Medicine, Yale-New Haven Hospital

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John T VanDeVoort, PharmD Regional Director of Pharmacy, Sacred Heart and St Joseph's Hospitals

John T VanDeVoort, PharmD is a member of the following medical societies: American Society of Health-System Pharmacists

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Michael J Verive, MD Medical Director, Pediatric Intensive Care, Department of Pediatrics, St Mary's Hospital for Women and Children

Michael J Verive, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Chest Physicians, Pediatric Sedation, and Society of Critical Care Medicine

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Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

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Note chocolate brown color of methemoglobinemia. In tubes 1 and 2, methemoglobin fraction is 70%; in tube 3, 20%; and in tube 4, normal.
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