Haemolysis usually occurs at a low to moderate level, at a rate at which a patient’s bone marrow can replace all or most of the destroyed cells, keeping the haemoglobin fairly stable, even if it is below normal levels. Sometimes heavier haemolysis occurs, resulting in more significant drops in haemoglobin and the red blood cells may need to be replaced via a blood transfusion. This is referred to as a haemolytic crisis and over time, patients will become familiar with what may trigger a crisis for them. Any form of stress to the body may trigger haemolysis.Some common stressors include:

Bacterial or viral infections	Lack of sleep
Exercise	Emotional upset
Certain foods, usually those containing high levels of fat	Alcohol
Other illnesses, injuries or surgery	Flying

Chronic haemolysis places continuous strain on vital organs, particularly the liver; kidneys; and heart, thus increasing the risk of serious and life-threatening complications such as liver and/or kidney failure; heart attack; stroke; deep vein thrombosis; Budd-Chiari Syndrome (a clot or clots in the hepatic vein of the liver); or blood clots in other veins or organs.

Clots are the most common complication of PNH and the leading cause of death among patients. This is a scary thing for a patient to face, but knowing the signs and symptoms of a clot and getting treatment as soon as possible can minimise the risk of further complication. If you experience swelling in the limbs or abdomen and severe and/or sudden onset of pain, you should seek medical advice immediately.