Health condition
Methaemoglobinaemia
Methaemoglobinaemia is a state in which altered haemoglobin cannot carry oxygen, causing bluish skin and low oximeter readings despite normal oxygen pressure; it may be inherited or triggered by drugs and chemicals, and severe acquired cases respond to methylene blue.
Why trust this guide
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Editorial team
Written by our editorial team from the UK sources listed on each page.
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Sourced from guidance
Checked against current NHS and UK specialist society guidance at the time of review.
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Current for 2026
Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.
Key facts
The essentials at a glance.
The symptoms to recognise, when to seek help, which specialist to see, and what treatment usually involves.
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Suspect it when oxygen saturations sit around 85% but do not improve with oxygen
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Common triggers include local anaesthetics (benzocaine, prilocaine), dapsone and nitrites
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Chocolate-brown arterial blood is a bedside clue; co-oximetry confirms the level
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Methylene blue is the antidote for significant acquired cases - but not in G6PD deficiency
Understanding the condition
What it is and what happens next.
What causes it, how it is diagnosed, and the treatment routes available in the UK.
What it is and how it feels
Haemoglobin carries oxygen only while its iron stays in the ferrous state; oxidising insults flip it to ferric methaemoglobin, which cannot bind oxygen and drags the rest of the molecule’s performance down with it. The result is cyanosis unresponsive to oxygen and a characteristic gap between what the pulse oximeter claims and what the patient’s blood gas shows. Inherited forms cause lifelong, usually well-tolerated blueness.
Diagnosis and treatment routes
Acquired episodes are dose-related emergencies at higher levels, treated by stopping the trigger and giving methylene blue, which recruits an alternative reducing pathway - one reason G6PD status matters, since that pathway fails in deficiency and methylene blue can then cause haemolysis. Congenital cases from cytochrome b5 reductase deficiency need little beyond avoiding oxidant drugs; the rarer haemoglobin M variants are managed with explanation and family testing. In many parts of the UK, routine NHS referrals for this kind of problem can take months, whereas an initial appointment with a private consultant is typically available within around two weeks.
Seeing a specialist
Who to see, and how quickly you can be seen.
The specialist for this condition is usually a consultant haematologist. Your GP can refer you on the NHS, or you can arrange a private consultation directly.
A quiet reminder
This guide is for information, not medical advice.
Your GP knows your history and can tell you which parts apply to you. If in doubt, see them - and seek urgent care for any of the emergency symptoms described above.