Paroxysmal nocturnal hemoglobinuria (PNH) is a rare blood disorder that happens when part of your immune system attacks and damages your red blood cells and platelets. Left untreated, PNH can cause hemolytic anemia, chronic kidney disease or thrombosis (blood clots). Healthcare providers treat PNH with medication that prevents blood cell damage.
Paroxysmal nocturnal hemoglobinuria (PNH) is a rare blood disorder named for a single symptom: Red/brown/dark urine noticed during late night or early morning trips to the bathroom. “Paroxysmal” means sudden; “nocturnal” means night; and “hemoglobinuria” refers to pee stained with blood. Your pee is dark because your immune system is breaking down your red blood cells. Healthcare providers call this hemolysis.
Dark-colored pee is only one of many PHN symptoms that may signal potentially serious illnesses. Left untreated, PNH may cause hemolytic anemia, chronic kidney disease or thrombosis (blood clots in your blood vessels). Healthcare providers treat PNH with medication that prevents blood cell damage.
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About 6 per 1 million people are diagnosed with PNH each year. This condition affects men and women between the ages of 30 and 40. Women are slightly more likely than men to develop PNH. Often, people who have bone marrow disorders like aplastic anemia or myelodysplastic syndrome develop paroxysmal nocturnal hemoglobinuria.
Both conditions cause blood in your urine. The difference is hematuria is red blood cells in your urine, while hemoglobinuria is hemoglobin in your urine. Hemoglobin is a protein in your red blood cells that makes blood look red.
PNH happens when a genetic flaw affects how your red blood cells and platelets work. The flaw launches a cascade of events that create serious and potentially life-threatening medical issues.
The cascade starts in your bone marrow, where your body makes stem cells that eventually become mature red blood cells, white blood cells and platelets. In PNH, a gene called PIGA in one stem cell mutates or changes into an abnormal stem cell. This cell divides and makes additional abnormal stem cells that become abnormal red blood cells and platelets.
Occasionally, proteins that help your white blood cells fight infection turn on your red blood cells. Healthcare providers refer to these proteins as the complement system.
Normal red blood cells have a protective shield of proteins that fends off complement system assaults. The PIGA gene is responsible for the red blood cells’ protective shield. When the PIGA gene mutates, it stops making the protective shields. Here’s what happens next:
Platelets are blood cells that help your body make blood clots. The mutated PIGA gene also affects stem cells that become abnormal platelets. The abnormal platelets make your blood clot more than it should. As a result, people who have PNA have an increased risk of life-threatening thrombosis or blood clots.
While paroxysmal nocturnal hemoglobinuria is named for one symptom, people who have PNH typically seek medical help because they have severe and persistent fatigue or tiredness that affects their daily lives. Other symptoms include:
Healthcare providers may use several tests to look for signs of PNH. Based on those test results, they may use a test called flow cytometry to examine your blood cells. Tests healthcare providers might use include:
Healthcare providers use targeted therapies called complement inhibitors that keep your complement system from destroying red blood cells.
Before this therapy was available, people with paroxysmal nocturnal hemoglobinuria needed regular red blood cell transfusions to treat anemia caused by PNH. At that time, people with PNH usually lived 10 to 22 years after their diagnosis. The only cure for PNH was to have an allogeneic stem cell transplant. Now, studies show people who receive this treatment can expect to live as long as someone who doesn’t have PNH.
Complement inhibitors have many side effects. Fortunately, these side effects wear off soon after people start treatment.
A genetic mutation causes PNH, which means you can’t prevent it.
There are treatments that stop PNH from damaging your red blood cells and platelets. Most people who have PNH develop anemia that requires additional treatment.
Even with treatment, people who have PNH need to take steps to prevent blood clots. For example, people who have PNH and need surgery are at risk for blood clots and serious bleeding during surgery. People who are pregnant and have PNH face health risks that affect them and the developing fetus.
A note from Cleveland Clinic
Paroxysmal nocturnal hemoglobinuria (PNH) is a rare blood disorder that happens when part of your immune system attacks and damages red blood cells and platelets. Fewer than 20 years ago, PHN was a debilitating disease treated with blood transfusions. Even so, PHN put people at risk for serious and sometimes life-threatening illnesses. Most people lived 10 to 22 years after their diagnosis.
But today, people with PHN receive innovative treatment that protects their blood cells and reduces their risk of serious illness. People with PHN can expect to live as long as someone who doesn’t have the disease. If you have paroxysmal nocturnal hemoglobinuria, your healthcare provider will explain your treatment options. Treatment doesn’t cure PHN, but it can keep the condition from creating serious medical issues.
Last reviewed by a Cleveland Clinic medical professional on 04/25/2022.
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