Paroxysmal Nocturnal Hemoglobinuria: A Glossary of Terms

Terms that can help you make sense of what is happening in the body when a person has PNH.

Learning about your diagnosis can be more complicated when important information is surrounded by unfamiliar terms.

Paroxysmal Nocturnal Hemoglobinuria (PNH) is a life-threatening blood disorder characterized by defective red blood cells that break apart, leading to complications like low blood cell counts, blood clots, and bone marrow failure.

PNH is a rare condition, affecting fewer than two people out of every million.

If you are diagnosed with any serious health condition, it is important to learn as much as you can about that condition.

This can be more complicated when a condition is rare—there is less available data and fewer case studies to inform patient education materials. It can also be more complicated when the information that is available is surrounded by unfamiliar terms.

Below is a list of terms associated with PNH that can serve as a reference when you are reading up on the condition and how it can be treated.

  • Paroxysmal. Paroxysmal symptoms refer to symptoms that are sudden and recurring, which describes the pattern of symptoms typical of PNH.
  • Nocturnal. Nocturnal refers to night. In many cases of PNH, hemoglobin can accumulate in the bladder while a person sleeps at night.
  • Hemoglobinuria. This refers to hemoglobin in the urine, which is a common symptom of PNH. Urine that contains hemoglobin will be dark in color.
  • Hemoglobin. An iron-rich protein found in red blood cells. Hemoglobin is needed to transport oxygen throughout the body and to clear carbon dioxide from the body.
  • Acquired disorder. Some health conditions are present at birth (congenital), others are acquired at a later point in a person’s life. PNH is acquired later in life and typically affects adults.
  • Anemia. A condition where the blood does not have enough red blood cells or hemoglobin. PNH causes hemolytic anemia, which occurs when red blood cells are broken down faster than the body can make more.
  • Thrombosis. Blood clots are one possible complication of PNH. Blood clots are clumps of coagulated blood that form in the veins. Thrombosis occurs when a blood clot blocks a vein or artery. It is the leading cause of death among people who have PNH.
  • Budd-Chiari syndrome. This refers to a blood clot that blocks a vein that drains blood from the liver. This is one of the most common sites for thrombosis in people who have PNH. Thrombosis in the head and abdomen are also common.
  • Stem cell. A type of cell that can mature into many different types of cells. Blood cells (including red blood cells, platelets, and white blood cells) begin as stem cells in the bone marrow, the spongy tissue found inside bones.
  • Bone marrow failure. Bone marrow failure occurs when the bone marrow is no longer able to produce blood cells. This is another potential complication of PNH.
  • Aplastic anemia. A type of bone marrow failure. Some cases of PNH evolve from aplastic anemia or as a side effect from treatment for aplastic anemia.
  • PIGA gene. PNH begins with mutations to this gene, which occurs inside stem cells found in the bone marrow. When this mutation occurs, stem cells produce red blood cells that break apart too easily. This mutation occurs due to a genetic defect, but not all people with this genetic defect will develop PNH.
  • Monoclonal antibody. These are lab-made proteins that attach to cells in the immune system and help the immune system work. There are many different types, which work in different ways. The medications that are used to treat PNH are monoclonal antibodies that bind to immune cells and prevent the destruction of red blood cells.
  • Allogenic stem cell transplant. A type of bone marrow transplant that is sometimes used to treat PNH—usually in very severe cases or in cases where a person with PNH does not respond to other treatments. Allogenic refers to stem cells that come from a donor.

Remember, PNH is a different experience for everyone. If you have questions about the condition or your diagnosis, your healthcare provider will be your best source of information.

Article sources open article sources

Johns Hopkins Medicine. "Paroxysmal Nocturnal Hemoglobinuria (PNH)."
National Organization of Rare Disorders. "Paroxysmal Nocturnal Hemoglobinuria."
MedlinePlus. "Paroxysmal nocturnal hemoglobinuria."
NCI Dictionaries. "Hemoglobin."
The American Academy of Family Physicians. "Patient Education: Anemia."
Johns Hopkins Medicine. "Hemolytic Anemia."
MedlinePlus. "Blood Clots."
Johns Hopkins Medicine. "Thrombosis."
Mayo Clinic. "Stem cells: What they are and what they do."
Christine A. Moore and Koyamangalath Krishnan. "Bone Marrow Failure." StatPearls. July 13, 2021.
Johns Hopkins Medicine. "Aplastic Anemia."
MedlinePlus. "PIGA gene."
Cleveland Clinic. "Monoclonal Antibodies."
Leukemia & Lymphoma Society. "Allogenic Stem Cell Transplantation."

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