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A condition in which the body does not have enough red blood cells; this may lead to fatigue and other symptoms.


Sometimes referred to as blood thinners, anticoagulants are drugs that decrease the clotting ability of blood and help prevent the formation of blood clots.

Aplastic anaemia

An immune disorder in which the bone marrow does not produce enough healthy blood cells, including red blood cells, white blood cells, and platelets. Patients with PNH sometimes also have aplastic anaemia.

Blood clots

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”).

Bone marrow

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

Chronic haemolysis

The destruction of red blood cells (haemolysis) over a long period of time (chronic).


Part of the immune system that destroys bacteria and other foreign cells. In PNH, complement is responsible for the destruction of red blood cells which lack specific protective proteins.


Difficulty or discomfort when swallowing.


A sense of difficulty with breathing resulting in “shortness of breath.”


An alternative name for a mature red blood cell.


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


Haemoglobin in the urine.
This is technical term for the dark “cola-coloured” urine which is sometimes seen in PNH. When the red blood cells are “lysed” or destroyed, as they are in PNH, haemoglobin is released from the red blood cells. When it is not all processed by the body’s metabolism and kidneys, it is sent out as waste and colours the urine a characteristic cola-brown colour.


The yellow discolouration of the skin and mucous membranes (eg. eyes). Jaundice is caused by the build-up of a pigment called bilirubin, which is produced when the body breaks down red blood cells.

LDH (Lactate dehydrogenase)

An enzyme (chemical messenger) which is increased in conditions where red blood cells destruction is increased (haemolysis).

Meningococcal infection

Infection caused by the bacterium Neisseria meningitidis (also named meningococcus). This infection can cause meningitis or overwhelming infection of the bloodstream (sepsis)

Myelodysplastic syndromes (MDS)

A group of blood disorders that all involve problems with the production of blood cells. Patients with PNH sometimes also have myelodysplastic syndromes.

Paroxysmal Nocturnal Haemoglobinuria (PNH)

A rare blood disorder in which red blood cells are chronically destroyed or haemolysed by the complement system. This can lead to severe anaemia, fatigue and thrombosis.

PNH clone

A “group” (or collection) of cells in the body which are affected by the genetic defect that causes PNH. These cells all come from the same parent cell in the bone marrow. Since the genetic defect lies in 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 determines how large or small the PNH clone is.

Red blood cells (RBCs)

Blood cells that carry oxygen using a protein complex called haemoglobin. PNH red blood cells are continually attacked and destroyed by the complement system because they are missing important protective proteins.

Stem cells

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

Thrombosis (thrombotic events)

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