Skip to content

Information and Resources

Paroxysmal Nocturnal Hemoglobinuria (PNH)

What Is Paroxysmal Nocturnal Hemoglobinuria?

When you have paroxysmal nocturnal hemoglobinuria (PNH), red blood cells in your body break apart before they should. It happens because the proteins that would normally protect them from your immune system are missing. Your immune system attacks the red blood cells and breaks them down.

You can get this rare blood disease at any age. You aren’t born with it; it happens over time. Although it can be life-threatening, there are treatments to help you feel better and, in some cases, cure it.

Recommended Related to

Types of Blood Disorders

 Blood disorders can affect any of the three main components of blood: Red blood cells, which carry oxygen to the body's tissues White blood cells, which fight infections Platelets, which help blood to clot Blood disorders can also affect the liquid portion of blood, called plasma. Treatments and prognosis for blood diseases vary, depending on the blood condition and its severity.

Read the Types of Blood Disorders article > >

PNH affects everyone differently. Some people have only minor problems, but for others, it's much more severe. The biggest concern is blood clots. About 40% of people with PNH have a blood clot at some point.


PNH comes from your genes, but you don't get it from your parents and you can't pass it on to your kids.

A change in a gene causes your bone marrow to make abnormal red blood cells. This change is called a mutation.

These blood cells don't have proteins that shield them from your immune system. Your immune system attacks them, breaking them down.

Some doctors believe PNH is related to weak bone marrow. People with a certain type of anemia, called aplastic anemia, are more likely to get PNH. The reverse is also true: People with PNH are more likely to get aplastic anemia. In aplastic anemia, your bone marrow stops making new blood cells.

Not everyone with PNH has aplastic anemia.


PNH gets its name from one of its more common symptoms. About half of people with PNH pass dark or bright red blood in their urine at night or in the morning. "Paroxysmal" means "sudden," "nocturnal" means "at night," and "hemoglobinuria" means" blood in the urine."

PNH symptoms are caused by these problems:

  • Broken red blood cells
  • Too few red blood cells (which can cause anemia)
  • Blood clots in your veins

You could have many symptoms or just a few. Usually, the more of the faulty PNH blood cells you have in your body, the stronger your symptoms will be.

Broken red blood cells and anemia may make you:

  • Feel tired and weak
  • Have headaches
  • Have shortness of breath
  • Have an irregular heartbeat
  • Have belly pain
  • Have trouble swallowing
  • Have pale skin
  • Bruise easily
  • Men may have trouble getting or keeping an erection.

The symptoms of blood clots depend on where the clot happens:


  • Red, painful, or swollen area

Arm or leg:

  • Sore, warm, and swollen limb


  • Pain and swelling
  • Warm to the touch


  • Bad headache
  • Trouble moving, talking, or seeing


  • Trouble breathing
  • Sharp chest pain
  • Coughing up blood
  • Sweating

Blood clots are the most serious complication of PNH. If you think you may have a clot, call your doctor.

Hot Topics

WebMD Video: Now Playing

Click here to wach video: Dirty Truth About Hand Washing

Which sex is the worst about washing up? Why is it so important? We’ve got the dirty truth on how and when to wash your hands.

Click here to watch video: Dirty Truth About Hand Washing

Popular Slideshows & Tools on WebMD

Solutions for 19 types.
MS Overview
Recognizing symptoms.
Woman running
Boost Your Metabolism.
build a better butt
How to build a better butt.
lone star tick
How to identify that bite.
young woman in sun
What to watch for.
brain scan with soda
Tips to kick the habit.
row of colored highlighter pens
Tips for living better.
stressed working woman
And how to fix them?
fat caliper
Check your BMI.
woman dreaming
What Do Your Dreams Say About You?
man with indigestion
How to keep yours at bay.

Pollen counts, treatment tips, and more.

It's nothing to sneeze at.

Loading ...

Sending your email...

This feature is temporarily unavailable. Please try again later.


Now check your email account on your mobile phone to download your new app.

Women's Health Newsletter

Find out what women really need.