Methemoglobinemia

Suspect methemoglobinemia when cyanosis, dyspnea, neurologic symptoms, tachycardia, or low SpO2 is out of proportion to cardiopulmonary examination findings, particularly when hypoxemia appears refractory to supplemental oxygen. Dark or chocolate-brown blood and a normal PaO2 despite low pulse oximetry strengthen the diagnosis; neither finding replaces co-oximetry. PubMed+1PubMedMethemoglobinemia - StatPearls - NCBI BookshelfPubMedMethemoglobinemia: from diagnosis to treatment - PubMed

Immediately stop the suspected oxidant medication or exposure, administer supplemental oxygen, and assess airway, ventilation, hemodynamics, mental status, ECG, hemoglobin concentration, and acid-base status. The clinical danger is functional anemia: ferric hemoglobin cannot bind oxygen, reducing effective oxygen-carrying capacity despite a measured total hemoglobin that may appear acceptable. Wolters Kluwer+2Wolters KluwerMethemoglobinemia: When to Suspect and How to Treat : Current Medical IssuesScienceDirectAcquired methemoglobinemia: A systematic review of reported cases - ScienceDirectPubMedMethemoglobinemia - StatPearls - NCBI Bookshelf

Escalate urgency when there is altered mental status, hemodynamic instability, significant anemia, cardiac or pulmonary compromise, concomitant carbon monoxide poisoning, or rapidly rising methemoglobin. These conditions reduce oxygen-delivery reserve and justify treatment at lower methemoglobin concentrations than in otherwise healthy patients. PubMedPubMedRecommendations for diagnosis and treatment of methemoglobinemia - PMC

Obtain co-oximetry on an arterial or venous blood gas in every patient with a credible clinical syndrome. Co-oximetry spectrophotometrically measures hemoglobin derivatives, including oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin, and methemoglobin, and is the preferred confirmatory test. Wolters Kluwer+3Wolters KluwerMethemoglobinemia: When to Suspect and How to Treat : Current Medical IssuesOxford AcademicLaboratory Assessment of Oxygenation in MethemoglobinemiaWolters KluwerSuccessful management of methemoglobinemia with oral... : MRIMS Journal of Health SciencesPubMedMethemoglobinemia: from diagnosis to treatment - PubMed

Do not rely on calculated arterial oxygen saturation, routine pulse oximetry, or PaO2 to exclude disease. A saturation gap—difference between SpO2 and co-oximetry-derived SaO2—greater than 5% suggests an abnormal hemoglobin species, including methemoglobin, carboxyhemoglobin, or sulfhemoglobin. Wolters KluwerWolters KluwerSuccessful management of methemoglobinemia with oral... : MRIMS Journal of Health Sciences

Interpret the methemoglobin percentage in clinical context rather than as an isolated antidote trigger. Acute acquired disease is generally less well tolerated than congenital disease because the rate of rise matters; congenital patients may have baseline concentrations of 20% to 40% with chronic cyanosis and relatively limited symptoms. Wolters Kluwer+1Wolters KluwerMethemoglobinemia: When to Suspect and How to Treat : Current Medical IssuesPubMedRecommendations for diagnosis and treatment of methemoglobinemia - PMC

Classify most new presentations as acquired when cyanosis begins recently after a medication, toxin, or environmental exposure. High-yield exposures include dapsone; benzocaine and other local anesthetics; nitrates and nitrites; nitroprusside and nitric oxide; sulfonamides; nitrofurantoin; antimalarials; rasburicase; and aniline dyes. accessdata fda+4accessdata fda[PDF] 209511Orig1s000 - accessdata.fda.govaccessdata fda[PDF] CENTER FOR DRUG EVALUATION AND RESEARCHWileyMethemoglobinemia and hemolysis in a patient with G6PD deficiency treated with rasburicasePubMedMethemoglobinemia - StatPearls - NCBI BookshelfPubMedRecommendations for diagnosis and treatment of methemoglobinemia - PMC

Pursue hereditary evaluation after acquired triggers have been excluded or when cyanosis is longstanding, began in infancy, recurs without exposure, or occurs in relatives. Family history of dusky skin or blue sclera and consanguinity favor congenital disease; cardiac and pulmonary right-to-left shunting remain competing causes of central cyanosis that require independent evaluation. PubMed+2PubMedSummary of Joint European Hematology Association (EHA) and EuroBloodNet Recommendations on Diagnosis and Treatment of Methemoglobinemia - PMCPubMedRecommendations for diagnosis and treatment of methemoglobinemia - PMCPubMedA blue blood toddler– a case report of methemoglobinemia and literature review - PMC

Measure cytochrome b5 reductase activity to distinguish hereditary CYB5R3 deficiency from acquired disease; it is the reference test for this branch point. Confirm congenital disease with molecular testing, which can identify CYB5R3-related disease and globin-gene variants causing HbM disease. Hemoglobin electrophoresis can help identify HbM variants. PubMed+2PubMedSummary of Joint European Hematology Association (EHA) and EuroBloodNet Recommendations on Diagnosis and Treatment of Methemoglobinemia - PMCPubMedRecommendations for diagnosis and treatment of methemoglobinemia - PMCPubMedA blue blood toddler– a case report of methemoglobinemia and literature review - PMC

Before rasburicase, obtain G6PD testing because G6PD-deficient patients are at risk for both hemolysis and methemoglobinemia. If methemoglobinemia follows rasburicase, monitor for delayed hemolysis; in one reported pattern, hemolysis developed more than 30 hours after methemoglobinemia. WileyWileyMethemoglobinemia and hemolysis in a patient with G6PD deficiency treated with rasburicase

For acquired methemoglobinemia meeting treatment thresholds, give intravenous methylene blue as first-line antidotal therapy unless contraindicated. Treatment is indicated at 20% methemoglobin in symptomatic patients and at 30% in asymptomatic patients; use lower thresholds in patients with reduced oxygen-delivery reserve. Wolters Kluwer+1Wolters KluwerSuccessful management of methemoglobinemia with oral... : MRIMS Journal of Health SciencesPubMedRecommendations for diagnosis and treatment of methemoglobinemia - PMC

Do not give methylene blue to patients with G6PD deficiency. FDA labeling identifies G6PD deficiency as a contraindication because treatment can cause severe hemolysis and severe anemia; methylene blue may also be ineffective because its reduction to the active form depends on adequate reducing capacity. fda+1fda[PDF] Table of Pharmacogenomic Biomarkers in Drug Labeling - FDAWileyMethemoglobinemia and hemolysis in a patient with G6PD deficiency treated with rasburicase

Avoid excessive cumulative methylene blue exposure. Doses greater than 7 mg/kg can themselves act as an oxidant and induce or worsen methemoglobinemia in susceptible patients. If severe hemolysis occurs, discontinue methylene blue and pursue alternative management. fda+2fda[PDF] Table of Pharmacogenomic Biomarkers in Drug Labeling - FDAWolters KluwerMethemoglobinemia: When to Suspect and How to Treat : Current Medical IssuesOxford AcademicMethylene blue-induced Hemolysis in a patient with lidocaine-induced Methemoglobinemia: a case report | Oxford Medical Case Reports | Oxford Academic

Use serial co-oximetry to document response and identify rebound. Rebound or incomplete resolution is specifically described after aryl-amine exposures such as aniline and sulfa drugs such as dapsone; continue monitoring through clinical and laboratory resolution rather than relying on transient improvement in cyanosis. fdafda[PDF] Table of Pharmacogenomic Biomarkers in Drug Labeling - FDA

After stabilization, patients with persistent elevation or a history consistent with congenital disease should have CYB5R activity measurement and molecular confirmation when available. This distinguishes CYB5R3 deficiency from HbM disease and provides the basis for counseling about inheritance, baseline cyanosis, and oxidant avoidance. PubMed+2PubMedSummary of Joint European Hematology Association (EHA) and EuroBloodNet Recommendations on Diagnosis and Treatment of Methemoglobinemia - PMCPubMedRecommendations for diagnosis and treatment of methemoglobinemia - PMCPubMedA blue blood toddler– a case report of methemoglobinemia and literature review - PMC

Do not treat chronic cyanosis solely to normalize a laboratory value. Patients with congenital methemoglobinemia can tolerate higher baseline methemoglobin concentrations than patients with acute acquired disease; treatment decisions should instead incorporate symptoms, baseline concentration, and comorbid conditions that impair oxygen delivery. Wolters Kluwer+1Wolters KluwerMethemoglobinemia: When to Suspect and How to Treat : Current Medical IssuesPubMedRecommendations for diagnosis and treatment of methemoglobinemia - PMC

Oral methylene blue has been used as maintenance therapy in congenital disease, while oral ascorbic acid reduces methemoglobin slowly and has been used in hereditary disease. Long-term pharmacologic decisions require individualized hematology input because the available evidence is largely based on reports and small series. Wiley+2WileyA rare cause of cyanosis: Congenital methemoglobinemia - Guedri - 2021 - Clinical Case Reports - Wiley Online LibraryWolters KluwerSuccessful management of methemoglobinemia with oral... : MRIMS Journal of Health SciencesPubMedCongenital Methemoglobinemia in a 33-Year-Old Patient: A Case Report on a Rare Presentation and a Review of the Literature - PMC