In PNH, a component of the immune system called the complement system, attacks and destroys red blood cells during a process called hemolysis.
Normally, red blood cells are protected from complement activity by a specific protein on their surface that blocks the activity of complement. In PNH, some red blood cells lack this protein. As a result, when these PNH red blood cells leave the bone marrow and enter the circulation, they are susceptible to destruction if complement becomes activated.
The destruction of red blood cells is called "hemolysis," (pronounced "hee-MOL-i-siss.") Hemolysis is the central cause of the signs and symptoms associated with PNH. In PNH, hemolysis is chronic, occurring even when symptoms are not present.
PNH and "hemolysis"
Red blood cells contain a protein called "hemoglobin" that carries oxygen from your lungs to the cells in your body to be used for energy. In PNH, hemolysis lowers the number of red blood cells, resulting in anemia.
In addition, chronic hemolysis releases the contents of red blood cells into the circulation, which can ultimately lead to disabling fatigue, muscle pain and blood clots. Blood clots interrupt normal blood flow and may cause serious problems like stroke. The release of hemoglobin from red blood cells can also get into the urine, and can cause the urine to become dark or red (hemoglobinuria).
Next: The Role of Hemolysis