Hearing that you or someone you love has Paroxysmal Nocturnal Hemoglobinuria (PNH) can be frightening, especially if you’ve never heard of it before. Because PNH is a rare disease, many patients and families leave their first appointment with more questions than answers.

The good news is that treatment for PNH has advanced dramatically over the past two decades. Today, many people with PNH are able to manage their disease successfully, work, raise families, travel, and live full, active lives.

This guide is designed to help you understand what PNH is, why it happens, how it is treated, and what you can expect moving forward.

What Is PNH?

Paroxysmal Nocturnal Hemoglobinuria (PNH) is a rare blood disorder that affects the body’s blood-forming stem cells.

In PNH, some stem cells develop a genetic change, or mutation, that causes the blood cells they produce to lack important protective proteins on their surface.

Without these protective proteins, part of your immune system—called the complement system—mistakenly attacks and destroys your own red blood cells.

This process is called hemolysis.

Think of your red blood cells as cars with protective bumpers. In PNH, those bumpers are missing, making the cells vulnerable to damage as they travel through your bloodstream.

Is PNH Cancer?

No.

PNH is not cancer.

It is a rare blood disease caused by a mutation in bone marrow stem cells that occurs during a person’s lifetime. It is not considered leukemia, lymphoma, or another type of cancer.

However, because PNH affects the bone marrow, it may occur alongside other bone marrow disorders such as aplastic anemia.

Is PNH Inherited?

No.

PNH is not inherited and is not contagious.

The genetic mutation develops in a person’s bone marrow during their lifetime and cannot be passed from parents to children.

Nothing you or your family did caused PNH.

What Causes PNH?

PNH begins with a mutation in a gene called PIGA in a single bone marrow stem cell.

As that cell multiplies, it creates a group of blood cells—called a PNH clone—that all carry the same mutation.

These cells lack protective proteins known as CD55 and CD59, making them vulnerable to destruction by the complement system.

Doctors still do not know exactly why this mutation occurs.

What Does “PNH Clone” Mean?

One of the first things many patients hear is the size of their PNH clone.

A PNH clone is simply the percentage of blood cells affected by the PIGA mutation.

For example:

A 5% clone means about 5% of certain blood cells have the mutation.
A 50% clone means about half of those blood cells are affected.
A 90% clone means most of those blood cells are affected.

A larger clone does not always mean more severe symptoms, but it can increase the risk of complications.

Your healthcare team will monitor your clone size over time.

What Happens When Red Blood Cells Break Down?

When red blood cells are destroyed, they release hemoglobin into the bloodstream.

Normally, hemoglobin stays safely inside red blood cells.

Too much free hemoglobin can:

Reduce nitric oxide, a molecule that helps blood vessels relax.
Contribute to fatigue.
Cause abdominal pain.
Cause swallowing difficulty.
Lead to muscle spasms.
Affect kidney function.
Increase the risk of dangerous blood clots.

Common Symptoms

PNH affects everyone differently.

Some people have very mild symptoms, while others experience significant daily challenges.

Common symptoms include:

Fatigue
Weakness
Shortness of breath
Pale skin
Rapid heartbeat
Dark or cola-colored urine
Headaches
Difficulty concentrating (“brain fog”)
Chest pain
Abdominal pain
Difficulty swallowing
Erectile dysfunction in men
Back pain
Kidney problems

Symptoms often come and go depending on the level of hemolysis.

Why Is My Urine Dark?

Many patients notice dark, reddish, or cola-colored urine.

This happens because destroyed red blood cells release hemoglobin into the bloodstream, which is eventually filtered by the kidneys and passed into the urine.

Despite the name “Nocturnal,” dark urine does not occur only at night or in the morning.

Many people with PNH never experience dark urine at all.

What Is the Biggest Risk of PNH?

The most serious complication is blood clots (thrombosis).

Blood clots are the leading cause of serious illness and death in untreated PNH.

Clots can develop in:

Legs
Lungs
Liver
Abdomen
Brain
Other veins and arteries

Prompt treatment has significantly reduced this risk.

Seek immediate medical attention if you experience sudden chest pain, difficulty breathing, severe abdominal pain, swelling in a limb, severe headache, or symptoms of a stroke.

How Is PNH Diagnosed?

Diagnosis usually involves:

Complete Blood Count (CBC)
Flow cytometry (the gold standard test)
Lactate dehydrogenase (LDH)
Haptoglobin
Bilirubin
Reticulocyte count
Kidney function tests
Iron studies
Bone marrow biopsy if another bone marrow disorder is suspected

Flow cytometry measures the percentage of blood cells that lack CD55 and CD59.

PNH and Aplastic Anemia

PNH and aplastic anemia are closely related.

Many patients with aplastic anemia have a small PNH clone.

Likewise, some people with PNH also have bone marrow failure consistent with aplastic anemia.

Doctors monitor both conditions because treatment decisions may differ depending on whether hemolysis, bone marrow failure, or both are contributing to symptoms.

Treatment Options

Treatment depends on:

Your symptoms
Clone size
Blood counts
Degree of hemolysis
Risk of blood clots
Overall health

Not every patient requires immediate treatment.

Complement Inhibitors

Modern PNH treatment focuses on blocking the complement system before it can destroy red blood cells.

These medications have transformed PNH care.

Examples include:

Eculizumab
Ravulizumab
Pegcetacoplan
Iptacopan
Danicopan (used in selected situations with other therapies)

These medications reduce hemolysis, improve quality of life, decrease transfusion needs for many patients, and dramatically lower the risk of blood clots.

Your hematologist will recommend the treatment that best fits your specific situation.

Blood Transfusions

Some patients require red blood cell transfusions when anemia becomes severe.

The need for transfusions often decreases after effective treatment begins.

Blood Thinners

Patients who have experienced blood clots may need anticoagulant medications.

Your healthcare provider will determine whether these medications are appropriate for you.

Bone Marrow (Stem Cell) Transplant

A stem cell transplant is currently the only treatment that can potentially cure PNH.

However, because transplantation carries significant risks, it is usually reserved for patients with severe bone marrow failure, difficult-to-control disease, or certain complications.

Most patients with PNH do not require a transplant.

Vaccinations and Infection Prevention

Some PNH medications increase the risk of serious infections caused by certain bacteria, particularly Neisseria meningitidis, which causes meningococcal disease.

Before starting complement inhibitor therapy, your healthcare team will recommend specific vaccinations and, in some cases, preventive antibiotics.

It is important to stay current with all recommended vaccines and to seek immediate medical attention if you develop a fever or symptoms of a serious infection while receiving complement inhibitor therapy.

Living With PNH

Many patients are able to continue normal daily activities after treatment begins.

Helpful habits include:

Stay hydrated.
Take medications exactly as prescribed.
Keep all follow-up appointments.
Report new symptoms promptly.
Stay physically active as tolerated.
Eat a balanced diet.
Get adequate sleep.

Learning to recognize changes in your symptoms helps you and your healthcare team manage the disease effectively.

Pregnancy and Family Planning

Many women with PNH have successful pregnancies, but pregnancy is considered high risk because of an increased chance of blood clots and other complications.

If you are planning a pregnancy or become pregnant, it is important to work closely with a hematologist and a maternal-fetal medicine specialist experienced in high-risk pregnancies.

Do not stop or change your medications without speaking with your healthcare team.

Mental and Emotional Health

Living with a rare disease can feel isolating.

Patients commonly experience:

Anxiety
Depression
Fear of complications
Financial stress
Uncertainty about the future

Connecting with others who understand the condition can make a significant difference.

Support groups, counseling, patient advocacy organizations, and trusted family and friends can all provide valuable support.

Questions to Ask Your Doctor

Consider asking:

How large is my PNH clone?
Do I currently have active hemolysis?
Am I at increased risk for blood clots?
Should I start complement inhibitor therapy?
What vaccinations do I need?
What symptoms should send me to the emergency room?
Will I need regular transfusions?
How often will my blood work be checked?
Do I also have aplastic anemia or another bone marrow disorder?
What are my long-term treatment goals?

Keeping Track of Your Care

Many patients find it helpful to keep a record of:

Blood test results
LDH levels
Hemoglobin levels
PNH clone size
Medication schedule
Vaccination dates
Transfusion history
Questions for appointments
Symptoms between visits

Being organized helps you and your healthcare team monitor changes over time.

A Message for Family and Friends

PNH symptoms are often invisible.

Someone living with PNH may appear healthy while dealing with significant fatigue, pain, or anxiety.

Support can include:

Attending appointments
Helping with transportation
Assisting during treatment days
Encouraging rest
Learning about the disease
Simply listening

Understanding what your loved one is experiencing can make a meaningful difference.

Looking Forward

The outlook for people with PNH has improved dramatically. Before modern complement inhibitor therapies, many patients faced serious complications and shortened life expectancy. Today, advances in treatment have transformed PNH into a condition that is often manageable over the long term.

While every patient’s journey is unique, many people experience improved energy, fewer complications, and a greatly reduced risk of life-threatening blood clots with appropriate treatment and regular follow-up. Ongoing research continues to expand treatment options and improve quality of life for people living with PNH.

Helpful Terms

Bone Marrow: The soft tissue inside bones where blood cells are produced.

Complement System: A part of the immune system that helps destroy bacteria and damaged cells but mistakenly attacks unprotected PNH blood cells.

Hemolysis: The destruction of red blood cells.

Hemoglobin: The oxygen-carrying protein inside red blood cells.

PNH Clone: The percentage of blood cells affected by the PIGA mutation.

Flow Cytometry: The specialized laboratory test used to diagnose and monitor PNH.

LDH (Lactate Dehydrogenase): A blood test that often rises when red blood cells are being destroyed.

Thrombosis: The formation of a blood clot inside a blood vessel.

Complement Inhibitor: A medication that blocks the complement system and protects red blood cells from destruction.

Remember

A diagnosis of PNH can feel overwhelming, but you do not have to face it alone. Learn about your condition one step at a time, build a strong relationship with your healthcare team, and stay engaged in your care. With today’s therapies, many people with PNH are living longer, healthier, and more active lives than ever before. There is every reason to look toward the future with hope.