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Paroxysmal nocturnal haemoglobinuria (PNH), explained | CION Cancer Clinics
PNH is a rare, acquired blood disorder in which the immune system bursts red blood cells. The usual signs are dark, cola-coloured urine, deep tiredness from low haemoglobin, and blood clots in unusual places such as the liver or brain. A blood test called flow cytometry confirms it. Treatment ranges from watching a small clone to complement-blocking medicines that stop the red cell breakdown. At CION Cancer Clinics, every leukaemia, MDS and MPN case is reviewed by our haematologist and discussed at a tumour board before a plan is agreed.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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The short answer
What is PNH, and what are the usual symptoms?
Paroxysmal nocturnal haemoglobinuria, or PNH, is a rare blood disorder in which the body's own immune defences break down red blood cells inside the blood vessels. The usual signs are dark, cola-coloured urine, deep tiredness from low haemoglobin, and blood clots in unusual places.
What goes wrong in the blood
Every blood cell comes from stem cells in the bone marrow. In PNH, some of those stem cells pick up a gene change during life. The red cells they make lack a protective coating. Without it, a part of the immune system called complement attacks and bursts them. This is not inherited, and it cannot be passed to your children.
What the long name means
"Paroxysmal" means it comes in bursts. "Nocturnal" means at night. "Haemoglobinuria" means haemoglobin in the urine. The name describes dark urine first thing in the morning, but many people do not have this pattern, so normal-looking urine does not rule PNH out.
Its link with bone marrow failure
PNH often appears alongside conditions where the marrow makes too few blood cells. Some people are found to have a small PNH clone during tests for low blood counts, even before any symptoms of red cell breakdown. If you are being checked for low blood counts, it is reasonable to ask whether a PNH test has been done.
Symptoms
Which symptoms point towards PNH?
Not everyone has all of these, and each can have more common causes. It is the combination that raises the question.
Red cell breakdown
Dark red, brown or cola-coloured urine, yellowing of the skin or eyes, and tiredness out of proportion to your day.
Often worse with
- Infections
- Surgery or heavy exertion
Low haemoglobin
Breathlessness on stairs, a racing heartbeat, headaches, pale skin and feeling faint. Some people need regular blood transfusions.
Muscle spasms in the gut and throat
Tummy pain, trouble swallowing, and in men, difficulty with erections. These happen when burst red cells use up a substance that relaxes smooth muscle.
Blood clots
Clots in the veins of the liver, the gut or the brain, as well as the legs. Clots are the most serious problem in PNH and need urgent care.
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Two situations that cannot wait
Go to the nearest emergency department now, or call 108, if someone with PNH has sudden severe tummy pain or a swelling belly, a severe headache, a painful swollen leg, chest pain or sudden breathlessness. These can be signs of a clot. If you are on a complement-blocking medicine, a fever, a stiff neck, a new rash or feeling suddenly very ill needs the same urgency. Show your treatment card and say you have PNH.
Getting a diagnosis
How is PNH diagnosed?
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First blood tests
A full blood count, a reticulocyte count, which shows how fast new red cells are being made, and tests of LDH, bilirubin and haptoglobin. Together these show whether red cells are being destroyed.
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Ruling out other causes
A Coombs test is usually negative in PNH, which helps separate it from immune conditions that also burst red cells. Iron, vitamin and kidney tests are often done too.
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Flow cytometry
This is the test that confirms PNH. A blood sample passes through a machine that checks whether red and white cells carry the missing protective proteins. It also measures the size of the PNH clone.
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A bone marrow test, if needed
If blood counts are low, a marrow sample checks whether a marrow failure condition is present alongside PNH.
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Scans for clots
An ultrasound or CT of the tummy, or a brain scan, is arranged if symptoms suggest a clot.
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On your report
What do the words on a PNH report mean?
- PNH clone size
- The share of your blood cells missing the protective proteins. A larger clone usually means more red cell breakdown.
- CD55 and CD59, or FLAER
- The markers flow cytometry looks for. Cells lacking them are PNH cells.
- LDH
- An enzyme released when red cells burst. A high level shows ongoing breakdown.
- Haptoglobin
- A protein that mops up free haemoglobin. A low level suggests red cells are being destroyed.
- Haemosiderin in urine
- Iron passed in the urine after long-term red cell breakdown.
Treatment
How is PNH treated?
The main treatment for PNH with symptoms is a complement-blocking medicine, which stops the immune attack on red cells. Not everyone needs it. A small clone with no symptoms may simply be watched with regular blood tests.
Complement-blocking medicines
Eculizumab and ravulizumab are given as drips into a vein at regular intervals. Newer medicines such as pegcetacoplan, given under the skin, and iptacopan, taken by mouth, act at a different point in the same system. These medicines lower red cell breakdown and the risk of clots. They are very costly, and access in India needs planning.
Because they weaken one of the body's defences, vaccines against meningococcal and some other infections are needed before starting, and sometimes preventive antibiotics too. Keep your vaccine record with your reports. You will carry a card saying you are on this treatment.
Other care
Blood transfusions, folic acid, blood thinners after a clot, and treatment of any marrow failure are often part of the plan. A stem cell transplant is the only treatment that can remove the PNH clone, but it carries serious risks and is usually considered only when marrow failure is severe. It does not suit most people with PNH alone. CION does not perform transplants; the haematology team can assess whether one is worth considering and coordinate a referral.
Never stop, skip or delay a complement-blocking medicine or a blood thinner on your own. Stopping suddenly can trigger severe red cell breakdown.Commonly believed
What do families often get wrong about PNH?
"Dark urine means a kidney stone or a urine infection."
Those are more common causes, but dark urine with tiredness and a low haemoglobin needs blood tests too. A quick urine strip test reacts to both haemoglobin and whole blood, so on its own it can mislead.
"PNH runs in the family, so the children should be tested."
PNH is not inherited. The gene change happens in marrow stem cells during life. Children do not need PNH testing unless they have their own symptoms.
"Iron tablets will fix the low haemoglobin."
Some people with PNH do lose iron, but iron alone does not stop red cells being destroyed. Take iron only if your haematologist advises it.
"The urine looks normal now, so the treatment can stop."
Clearer urine usually means the medicine is working. Stopping it lets the breakdown return, sometimes severely. Any change must be decided with your team.
Questions we are asked
Common questions about PNH
Is PNH a blood cancer?
No. PNH is a rare acquired blood disorder, not a cancer. It is looked after by haematologists because it starts in the bone marrow, is linked with marrow failure conditions, and needs specialised tests and medicines. In a small number of people, related marrow conditions can develop over time, which is one reason for regular review.
Why is it called nocturnal if my urine is dark during the day?
The name was given long ago, when doctors noticed dark urine in the morning. In reality, red cell breakdown goes on day and night, and many people never notice a morning pattern. The timing does not change the diagnosis or the treatment.
Can PNH go away on its own?
In a small number of people, the PNH clone shrinks over years. For most, it stays. This is why a small clone without symptoms is often watched with regular tests, while PNH with symptoms is usually treated. Your haematologist will review the clone size over time.
Is it safe to get pregnant with PNH?
Pregnancy with PNH carries a higher risk of clots and needs careful planning. Talk to your haematologist before trying to conceive. Many women have had safe pregnancies with close joint care from a haematologist and an obstetrician.
Why do I need vaccines before treatment?
Complement-blocking medicines weaken the body's defence against certain bacteria, especially the ones that cause meningitis. Vaccines lower that risk but do not remove it, which is why any fever on treatment needs urgent medical attention. Your team will arrange the right vaccines and timing.
Will I need blood transfusions?
Some people do, especially before treatment starts or if marrow failure is also present. Complement-blocking medicines often reduce or remove the need for transfusions. Your team decides on transfusions based on your symptoms and repeat blood tests, not on one result.
Are PNH medicines available and covered in India?
Access varies and the medicines are costly. Coverage under Aarogyasri, PM-JAY, CGHS, ECHS, EHS or cashless insurance differs by scheme and changes over time. Ask your haematologist about access programmes, and call the helpline so we can help you check your current cover.
What should I bring to a first appointment?
Bring every blood count, any flow cytometry report, urine tests, scans, bone marrow reports and a list of medicines, including any blood thinners or iron. Note when dark urine, tiredness or pain first began, and any past clots.
Your Haematologist
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Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
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Where to find us
Our centres in and around Hyderabad
Addressed by landmark, because that is how this city navigates. A haematology consultation can be booked at any of these centres through one helpline, and your team will tell you where each test or treatment takes place.
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Sources
- National Heart, Lung, and Blood Institute — Blood Tests
- NHS — Deep vein thrombosis (DVT)
- NHS — Meningitis
- NHS — Blood transfusion
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Talk to us
Dark urine, low haemoglobin and no clear cause?
Share your blood reports with us. CION's haematology team will look at whether PNH has been properly tested for and what should come next. One helpline serves every CION centre.