What are the symptoms of PNH?

PNH can cause a variety of symptoms. You may have many of these symptoms, or just one or two. And you may experience a new symptom at any point in the course of your illness. Some people have more severe symptoms than others.

The symptoms you have with PNH are caused by one of the following:

  • Hemolysis – the breaking apart or destruction of red blood cells
  • Thrombosis – blood clots
  • Low blood cell count – not having enough of a type of blood cell

Each of these health problems can cause certain symptoms as described below.


Hemolysis is the breaking apart of red blood cells.

What causes hemolysis?
Hemolysis happens when the complement system becomes more active and attacks your PNH red blood cells. The complement system usually attacks only foreign objects, such as viruses and bacteria. But, because PNH cells are damaged, it sees them as foreign and attacks them too, causing them to burst.

What are the symptoms of hemolysis?
When your PNH red blood cells break apart, their hemoglobin is released into your plasma. Hemoglobin is the red part of red blood cells. Its job is to carry oxygen around your body. The release of hemoglobin can cause a number of symptoms:

  • Your urine may get darker; or it may not darken at all
  • You may have a low red blood cell count (anemia) which can cause you to:
    • Feel very tired
    • Have headaches
    • Have trouble breathing when you exercise
    • Have an irregular heartbeat

What are the symptoms of severe hemolysis?

If you have severe hemolysis, hemoglobin may be quickly released into your bloodstream. This can cause a number of symptoms:

  • You may feel very tired.
  • The hemoglobin may bind with and remove nitric oxide from your system. Nitric oxide helps your muscles stay smooth and relaxed. A shortage of it can cause muscle spasms in certain parts of your body: 
    • You may have anything from mild to severe pain in your abdomen or belly area.
    • You may have spasms in your esophagus which is a "tube" in your throat that goes from your mouth to your stomach; the spasms can make it hard to swallow.
    • Men may have trouble getting or keeping an erection (be impotent).


Thrombosis is a blood clot in a vein. It is often simply called a blood clot.

Who gets blood clots?

At least 1 out of 3 people with PNH gets blood clots. 

Why are blood clots so common for people with PNH?

Scientists are not sure exactly why people with PNH are more likely to get blood clots. But some believe that PNH patients have abnormal platelets that are too "sticky." This means the platelets make clots too easily.

Plus, many people with PNH have a shortage of nitric oxide. Nitric oxide helps prevent blood clots by making it harder for platelets to stick together. Hemolysis – another symptom of PNH – can cause a shortage of nitric oxide.

What are the symptoms of blood clots?

The symptoms of blood clots depend on where the clots occur. People who are otherwise healthy and don't have PNH sometimes get blood clots in the veins of the leg. But people with PNH tend to get blood clots in other parts of the body, such as in the brain or abdomen (belly area).

Blood clot in abdomen (belly area)

You may get a blood clot in your abdomen, or belly area. That's the area below your chest and above your hips. Here are some places in the abdomen where you may get a blood clot:

  • You may get a blood clot in your spleen.
  • You may get a blood clot in the major vein that leaves your liver; this is called Budd-Chiari syndrome.
  • Your intestine (bowel) may not get enough blood; this is called ischemia.

If you have a blood clot in your abdomen:

  • You may have fluid and swelling in the belly area; this is called ascites.
  • The area where the clot is may feel warm to the touch.
  • The area where the clot is may be painful.

If the blood clot in your abdomen is not treated:

  • Part of your intestine may die (dead bowel)
  • Your liver may be damaged and stop working

Blood clot in brain

You may get a blood clot in the veins covering your brain. If this happens:

  • You may get a very bad headache.
  • Your brain may not work as well as usual; you may have trouble speaking, seeing, or moving parts of your body.

Blood clot in skin

You may get a blood clot in the veins of your skin. If this happens:

  • Your skin in that area may get red, puffy, warm, or painful

Blood clot in arm or leg

You may get a blood clot in the veins of your arm or leg. If this happens:

  • That limb may get warm, puffy, or painful

Blood clot in lung

Sometimes, a blood clot breaks off and travels to your lung. This is called a pulmonary embolism (PULL-muh-nerr-ee EM-buh-liz-um). If you have a pulmonary embolism:

  • You may have a sharp pain in your chest; it may get worse when you breathe deeply
  • You may have trouble breathing (shortness of breath) or you may start breathing fast
  • You may suddenly feel anxious
  • You may cough up some blood
  • You may feel dizzy; you may even faint
  • You may sweat a lot

How do I find out if I have a blood clot?

To diagnose a blood clot, your doctor may take pictures of your insides using:

Or, your doctor may order a lab test called D-dimer. It's also called Fragment D-Dimer, or Fibrin degradation fragment.

Low Blood Counts

The symptoms of PNH are often caused by low blood cell counts. The symptoms depend on which type of blood cell is affected. For PNH, the most common shortage is red blood cells.

Low Red Blood Cell Count

A low red blood cell count is called anemia. Red blood cells carry oxygen from your lungs to the rest of your body. A low red blood cell count causes fatigue and tiredness.

Low White Blood Cell Count

A low white blood cell count is called neutropenia. White blood cells fight infections in the body by attacking and killing bacteria and viruses. A low white blood cell count can increase the risk for infections.

Low Platelet Count

A low platelet count is called thrombocytopenia. Platelets help blood to clot and stop bleeding. A low platelet count can lead to bleeding problems and cause you to bruise easily.

Learn more about the symptoms of low blood counts.