Glossary of Terms 

Anemia
A condition in which your body does not have enough
red blood cells—the oxygen-carrying component of your
blood—causing fatigue.

Antibodies
Proteins produced by your immune system that find and attack invading cells, like bacteria.

Anticoagulant
Medication that slows the formation of blood clots, which may be a problem for patients with PNH.

Antigen
Molecules that stimulate an immune response. Antigens bind to immune cells. Those cells then “present” these antigens to other parts of the immune system, which leads to one of several different types of responses. Antigens are generally things that are considered foreign by the body and are destroyed.

Aplastic anemia
An immune disorder in which your bone marrow does not produce enough healthy red blood cells. Patients with PNH sometimes also have aplastic anemia.

Aspartate transaminase (AST)
Enzyme that is released by cells into blood when certain tissues or organs are damaged. AST is found in red blood cells, liver and heart cells, and muscle tissue. High blood levels of AST may be directly related to the amount of damage to particular cells.

Autoimmune disease
When your immune system does not recognize your body’s own healthy tissues and launches an immune response against its own cells. PNH is a type of autoimmune disease.

Bilirubin
A reddish-yellow waste product that is formed when a red blood cell dies. Too much bilirubin can be a consequence of the hemolysis in PNH and causes jaundice.

Bone marrow
Soft tissue inside your large bones. Bone marrow contains stem cells, which go on to form red blood cells, white blood cells, and platelets in a process called hematopoiesis.

Bone marrow aspiration
A medical test in which a small amount of liquid from your bone marrow is extracted by a needle inserted into the back of your hip. This test is often performed before a bone marrow biopsy.

Bone marrow biopsy
A medical procedure in which a small cylindrical piece of solid bone is removed. May help in diagnosing PNH.

Bone marrow transplantation (BMT)
The process of replacing defective bone marrow with the body’s own (autogeneic) or someone else’s (allogeneic) bone marrow. This process can potentially eliminate all PNH cells from the bone marrow, but it involves significant risks and side effects.

Budd-Chiari syndrome
A clot within the hepatic vein, a major blood vessel in the liver. This is an unusual place for a clot and can be indicative of PNH. Anyone with Budd-Chiari syndrome should be screened for PNH.

CD59
Protein on the outside of the cell membrane that protects cells from lysis by complement. This protein is absent from PNH blood cells because of missing anchor proteins.

Clot
When many platelets in the blood stick together, they form a blood clot. These clots can block blood flow in the veins and arteries, depending on their size and location (see Thrombosis).

Coagulation
When a liquid turns into a solid, such as when a blood clot is formed.

Complement
Part of your immune system that destroys bacteria and other foreign cells. In PNH, it is responsible for the destruction of red blood cells that lack specific protective proteins (see CD59).

Complete blood count
Tests performed on a small amount of your blood that can provide information about the amount of each type of blood cell.

Cytopenia
A deficiency of any type of cell in your blood.  Anemia, a common symptom of PNH, fits into this category.

Cytotoxic
Damaging to cells.

Dysphagia
The medical term for difficulty swallowing, which can be experienced by patients with PNH.

Dyspnea
The medical term for shortness of breath, which can be experienced by patients with PNH.

Enzyme
A kind of protein that helps the body function. Almost all processes in a cell need enzymes in order for that process to occur at a reasonable rate.

Erythrocyte
Another name for a mature red blood cell.

Flow cytometry
A sensitive laboratory technique used to count and sort cells and their constituents. Today, this is the primary method used to diagnose PNH.

Free hemoglobin
Hemoglobin that has been released from red blood cells.

Gene
Genetic information that encodes essential proteins. This information, which is inherited from its parent cell, determines the characteristics of a cell.

Glycosylphosphatidylinositol (GPI)
An important type of anchor that links proteins to the cell surface. PNH cells lack GPI-anchored proteins. Without these GPI anchors, certain extracellular proteins, such as CD59, are missing from the surface of cells, leaving them vulnerable to destruction.

GPI anchor proteins
Proteins that are attached to the cell surface by an anchor called GPI. In PNH, the GPI-anchored proteins are missing, which causes red blood cells to be destroyed by the complement system.

Granulocyte
A name for some types of white blood cells because they have special “granules” that help fight infection.

Ham’s test
One of the first tests developed for PNH, Ham’s test looks for increased fragility of red blood cells in a mild acid. This test is no longer used as the primary diagnostic test for PNH, as there are more accurate tests now available.

Haptoglobin
A protein in the blood that helps to remove free hemoglobin from your body. In PNH, there is often not enough haptoglobin to “clean up” all the hemoglobin released from the destroyed red blood cells, resulting in discolored urine and other consequences of PNH.

Hematocrit
The amount of your blood volume that is occupied with
red blood cells.

Hematopoiesis
The production of blood cells, which occurs in your bone marrow. The anemia caused by red blood cell destruction in PNH can be made worse if hematopoiesis is not sufficient.

Hemoglobin
The brownish-red substance in red blood cells that carries oxygen throughout your body. Responsible for the characteristic dark urine seen in PNH.

Hemoglobinuria
Hemoglobin in the urine. This is the technical term for the “cola-colored” urine seen in PNH. When the red blood cells are lysed, or destroyed, as they are in PNH, hemoglobin is released from the red blood cells. When it is not all processed by the body’s systems, it is sent out as waste and gives the urine a characteristic
cola-brown color.

Immunocompromised
A condition in which the immune system is not working properly, making the body more susceptible to infections.

Intravascular hemolysis
The destruction of red blood cells mediated by the complement system in PNH.

Jaundice
Yellowing of the skin and the whites of the eyes due to too much bilirubin in the blood. Since bilirubin builds up when there is hemolysis, jaundice can occur in patients with PNH.

Lactate dehydrogenase (LDH)
Enzyme that is found in many organs in the body, and is especially abundant in red blood cells. High levels of LDH can indicate that many red blood cells are being broken down, releasing LDH into the blood stream, and serving as a marker for intravascular hemolysis in patients with PNH.

Lymphocyte
A particular kind of white blood cell that regulates the body’s immune response and is extremely important in fighting infection. There are two types of lymphocytes: T cells and B cells.  

Lysis
The act of destroying a cell. Red blood cells are lysed by complement in patients with PNH.

Microcytic anemia
Characterized by small red blood cells, microcytic anemia occurs when there is too little hemoglobin, which causes cell division within the marrow to occur for longer than normal, resulting in smaller cells.

Monoclonal antibodies
A group of antibodies that recognize and bind to a specific site on a protein. Depending on the antibody, this may stop the activity of the protein. Medicines in the form of monoclonal antibodies produced by recombinant technology for administration to humans may be useful in fighting illnesses of all kinds.

Myelodysplastic syndromes (MDS)
A group of blood disorders that all involve problems with the production of blood cells. PNH is often found in conjunction with myelodysplastic syndromes.

Neutropenia
A deficiency of neutrophils in the blood. This deficiency is dangerous because it leaves the body with weakened defenses
against infection.

Neutrophil
A type of immune cell that attacks invading cells and is found throughout the body.

Nitric oxide
An important molecule that acts throughout your body, regulating things such as smooth muscle tone. Too little nitric oxide in the bloodstream may cause dangerous clots to form, dysphagia, abdominal pain, high blood pressure, and erectile dysfunction, among other conditions, all of which are common in PNH.

Packed RBCs
A concentrated blood product in which plasma has been removed from the blood to make transfusions easier and faster.

Pancytopenia
A reduction in all of the formed elements of the blood.

Paroxysmal
Relating to a period during which symptoms become worse or exaggerated. PNH patients may notice their urine becomes dark and their symptoms become more severe during these episodes,
or paroxysms.

Paroxysmal nocturnal hemoglobinuria (PNH)
A rare blood disorder that destroys red blood cells. Signs and symptoms can include thrombosis, anemia requiring transfusions, disabling fatigue, and other health-related conditions that can affect quality of life.

Phagocytosis
The process by which white blood cells surround and kill
invading cells.

PIG-A
The gene that forms the blueprint of the GPI anchor which tethers important proteins to the surface of cells. PNH is caused by a defect in this gene.

Platelets (thrombocytes)
Cells in your blood that are essential for clotting. Platelets help stop bleeding when you’ve cut yourself, block blood flow inside blood vessels, but in certain disease states, they may stick together and form a clot.

PNH clone
A group of cells in your body that are affected by the genetic defect that causes PNH. These cells all come from the same parent cell in your bone marrow. Since the genetic defect lies in the parent cell, all cells derived from the parent cell, including red blood cells, white blood cells, and platelets, are affected. The number of cells affected by PNH determine how large or small your PNH clone is, often dictating how severe your condition becomes.

Protein
An important component of all living cells. There are many types of proteins, like enzymes and antibodies, and they are all necessary for normal function.

Red blood cells (RBCs)
Blood cells that carry oxygen using a protein complex called hemoglobin. PNH red blood cells are continually attacked and destroyed by the immune system because they are missing important protective proteins.

Reticulocytes
Young red blood cells found mostly in the bone marrow. The reticulocytes of patients with PNH are often missing proteins
such as CD59.

Sequelae
The consequences of a medical condition like PNH. Abdominal pain, difficulty swallowing, and erectile dysfunction can be
sequelae of PNH.

Serum
The clear, yellow liquid that separates from blood after clotting has occurred. Serum can be studied to reveal much about the patient, including whether they may have PNH.

Stem cells
Cells produced in your bone marrow that can become red blood cells, white blood cells, or platelets. PNH is a disease that originates in the stem cells.

Sucrose hemolysis test
A test for PNH that involves placing red blood cells into a solution that will cut or lyse them if they are affected by PNH.

Thrombosis
The formation or development of a blood clot that often blocks blood from flowing through a vessel. In PNH, blood clots can form in unusual sites, such as in vessels in the abdomen (see Clot).

Transfusion
A process performed by a health care professional that transfers donated blood or blood components into your bloodstream. It can replace some of the red blood cells you have lost from PNH and can therefore help with anemia.

Urinalysis
A test performed on the urine. A urinalysis is often part of the testing used when a patient is suspected of having PNH.

White blood cells
Immune cells which exist as different types (neutrophils, eosinophils, basophils, lymphocytes, and monocytes). White blood cells are part of the immune system and they destroy invading cells.