Getting to Know PNH Warning Signs

Medically Reviewed by Michael W. Smith, MD on March 23, 2021
2 min read

Because paroxysmal nocturnal hemoglobinuria (PNH) is a rare blood disorder that many people don’t know about, it may take someone months or years to get a proper diagnosis.

About half of people with PNH have a telltale symptom: Reddish or dark-colored pee. This happens because the disorder causes red blood cells to break apart, which releases bright red hemoglobin. The body gets rid of this hemoglobin through the urine.

If you tell your doctor about red or dark-colored pee, it may make PNH easier to diagnose. But about half of people don’t have that symptom.

But PNH has other signs that could help you or your doctor zero in on it:

In people with PNH, part of your immune system targets abnormal red blood cells, breaking apart those cells. This happens when a gene (called PIGA) mutates in the bone marrow’s stem cells. When the stem cells have mutations, they make red blood cells that don't have an important protein that usually keeps them safe from the immune system.

When red blood cells break apart, they may cause dark-colored urine, along with:

  • Muscle spasms
  • Trouble swallowing
  • Erectile dysfunction
  • Stomach pain
  • Headaches
  • Irregular or fast heartbeat
  • Chest pain
  • Trouble breathing during exercise


When red blood cells are destroyed faster than the body can replace them, you might get anemia, a low count of red blood cells. People with PNH and anemia could have:

  • Headaches
  • Lack of energy
  • Shortness of breath
  • Trouble breathing during or after exercise
  • Irregular heartbeat or heart palpitations
  • Pale skin
  • Dizziness or lightheadedness
  • Crankiness
  • A need to sleep more
  • Weight loss


Doctors aren’t sure why, but people with PNH often form blood clots too easily. It may be because people with PNH make abnormal blood platelets, which leads to more clotting.

These can be dangerous, because they keep blood from flowing properly and carrying oxygen around your body. Blood clots might also block the blood flow to different organs completely.

That could lead to a heart attack, stroke, liver damage, or organ failure.

What might signal a blood clot? If a blood clot affects your:

  • Arm or leg, it may become sore, warm, and painful
  • Liver, you could get jaundice (yellow skin and eyes), belly pain, or liver problems
  • Brain, it may cause headaches or problems with mental skills
  • Lungs, you might have trouble breathing, shortness of breath, heart palpitations, or chest pain


In addition to red blood cells, bone marrow stem cells make blood platelets and white blood cells. In some people with PNH, the mutated bone marrow stem cells don’t make enough healthy platelets. This may cause clotting problems. You may have:

  • Easy bruising
  • Signs of bleeding under your skin (such as small red spots)
  • Heavy bleeding, even from minor cuts or scrapes
  • Trouble stopping the bleeding from minor cuts or scrapes
  • Nosebleeds
  • Gums that bleed easily after dental work or brushing
  • Heavy menstrual periods