Skip to main content

Health condition

PNH deep dive

Paroxysmal nocturnal haemoglobinuria (PNH) is an acquired stem cell disorder in which blood cells lack protective surface proteins, causing red cell destruction, dark urine, fatigue and a strong tendency to clot; modern complement inhibitors have transformed its outlook.

Why trust this guide

  • 01

    Editorial team

    Written by our editorial team from the UK sources listed on each page.

  • 02

    Sourced from guidance

    Checked against current NHS and UK specialist society guidance at the time of review.

  • 03

    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.

  • Classic clues are dark (cola-coloured) urine, marked fatigue and unexplained clots

  • Diagnosed with a flow cytometry blood test measuring the size of the PNH clone

  • Closely linked to aplastic anaemia and bone marrow failure

  • Complement inhibitor treatment dramatically reduces haemolysis and clot risk

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

PNH begins with a mutation in the PIGA gene in a single marrow stem cell, producing blood cells that lack the anchored proteins normally shielding them from the complement system - part of the body’s innate immunity. Unprotected red cells are destroyed continuously, with surges overnight or during infections, releasing free haemoglobin that darkens the urine, drives fatigue, and injures blood vessels.

Diagnosis and treatment routes

Thrombosis in unusual sites - hepatic, abdominal or cerebral veins - is the most dangerous feature. Treatment has been revolutionised by complement inhibitors, from eculizumab and ravulizumab to newer oral and proximal-pathway agents, which control haemolysis and largely abolish clot risk in treated patients. Care is coordinated through designated PNH specialist centres in the UK, and anyone with a significant clone should be linked to one. 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.

Frequently asked

Common questions about PNH deep dive.

Quick, plain-English answers to what people ask us most.

  • What is PNH (paroxysmal nocturnal haemoglobinuria)?

    PNH is a rare, acquired blood disorder in which red blood cells become vulnerable to destruction by part of the immune system, leading to anaemia, blood clot risk, and other complications.

  • What causes PNH?

    It's caused by an acquired genetic mutation in blood stem cells (not inherited from parents), which leaves red blood cells lacking certain protective proteins, making them susceptible to destruction.

  • What are the symptoms?

    Fatigue, dark urine (particularly noticeable in the morning), abdominal pain, difficulty swallowing, and an increased risk of blood clots are characteristic symptoms, though presentation varies between individuals.

  • Is PNH dangerous?

    Yes, it can be serious, primarily due to the risk of blood clots, which can occur in unusual locations and be life-threatening, alongside the effects of chronic anaemia and, sometimes, bone marrow failure.

  • Is PNH hereditary?

    No, it's an acquired condition arising from a mutation in blood stem cells during a person's lifetime, not something passed down from parents or passed on to children.

  • Can PNH be treated?

    Yes, targeted medications (complement inhibitors) have transformed treatment, significantly reducing red cell destruction and clot risk; in some cases, bone marrow transplant may be considered as a potential cure.

  • How is PNH diagnosed?

    A specific blood test called flow cytometry, which detects the missing protective proteins on blood cells, confirms the diagnosis, alongside other blood tests assessing anaemia and blood cell destruction.

  • How long does treatment need to continue?

    Complement inhibitor treatment is typically needed long-term, often for life, to keep the condition well controlled and reduce the ongoing risk of complications such as blood clots.

  • PNH vs other causes of anaemia — what's the difference?

    Common anaemia causes like iron deficiency don't typically cause dark urine or the specific pattern of blood clot risk seen in PNH; the flow cytometry blood test specifically identifies PNH when it's suspected.

  • When should I see a specialist, and how quickly can I be seen privately?

    See a haematologist for unexplained anaemia, dark urine, or unusual blood clots. Private specialist assessment is typically available within about two weeks, considerably faster than standard NHS haematology referral waiting times.