Paroxysmal nocturnal hemoglobinuria is a rare acquired blood disorder that affects red blood cells and can lead to anemia, blood clots, and other complications. It develops when a change in a blood-forming stem cell causes certain blood cells to become vulnerable to destruction by the complement system.
Paroxysmal nocturnal hemoglobinuria (PNH) is an uncommon acquired disorder of the blood-forming stem cells in the bone marrow. It is not usually inherited or passed from parents to children. PNH can affect red blood cells, white blood cells, and platelets and may occur alongside other bone marrow disorders. The condition results from a genetic change acquired in a stem cell, which causes blood cells to lack certain protective proteins. Without these proteins, red blood cells can be more easily damaged by the complement system, part of the body's immune defense.
PNH develops because of an acquired mutation in the PIGA gene within a blood-forming stem cell. This mutation interferes with the production of proteins that normally protect blood cells from complement-mediated destruction. As the affected stem cell produces more blood cells, a population of cells with increased vulnerability can develop.
The severity and combination of symptoms differ from person to person. Some people have primarily anemia, while others may experience significant complications related to abnormal blood clotting.
Common symptoms and features can include:
Although the name includes the word "nocturnal," hemolysis does not necessarily occur only at night. Urine discoloration may also be absent even when red blood cell destruction is taking place.
Doctors may consider PNH when a person has unexplained hemolytic anemia, unusual blood clots, or certain bone marrow abnormalities. Diagnosis is generally confirmed through specialized laboratory testing. Flow cytometry is particularly important because it can detect blood cells that lack proteins associated with PNH.
Evaluation may also include blood counts, tests for hemolysis, kidney function testing, and examination of the bone marrow when clinically appropriate.
Treatment is individualized according to the person's symptoms, blood counts, complications, and overall health. Management may include:
People receiving complement-inhibiting medicines may require specific vaccination and infection-prevention measures because complement plays an important role in defending against certain infections. Treatment decisions should therefore be made with a qualified hematologist.
PNH is a chronic condition, but advances in diagnosis and treatment have substantially improved management for many patients. Regular medical follow-up can help identify changes in blood counts, hemolysis, kidney function, and clotting risk. Anyone experiencing symptoms such as severe abdominal pain, chest pain, sudden breathing difficulty, neurological symptoms, or signs of a blood clot should seek prompt medical attention. Information about PNH should be used for education and discussion with healthcare professionals rather than as a substitute for individualized medical care.