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There can be a large variation in the signs and symptoms of PNH both between patients and in the same patient at different times. Some people exhibit no symptoms and others may be affected by a number of very different ones as well as complications. Patients with no or few symptoms can still suffer from complications. Over time, the symptoms experienced by a PNH patient can change. Some patients only experience symptoms when an episode of severe haemolysis is occurring (which is usually triggered by an infection) and others may experience symptoms all the time.

Some common signs and symptoms are listed below:


Red, dark or black urine caused by free haemoglobin in the urine. This occurs due to the destruction of red blood cells by the complement part of the immune system which causes them to burst. When the red cells burst this releases haemoglobin into the blood plasma which then overflows through the kidneys into the urine. Nature has created haemoglobin to be well contained within red cells and it is very harmful/toxic when it is released. “Haematuria” with which haemoglobinuria can be confused, is a condition in which intact (rather than burst) red cells appear in the urine and is more commonly due to diseases of the urinary bladder or kidney.


Anaemia is a low red blood cell count. Red blood cells carry oxygen from your lungs to the rest of your body. Anaemia is common in PNH patients due to the constant destruction of their red blood cells. Anaemia can also be aggravated by bone marrow failure which can also occur in PNH patients. Anaemia causes increased fatigue, tiredness and breathlessness.


Breathlessness can be caused by anaemia as well as by increased blood flow and the subsequent increase in pressure in the blood vessels of the lungs (pulmonary hypertension) which can occur in PNH patients. If sudden breathlessness occurs, it is important to get this checked out to make sure this is not due to a complication.


Bruising can be caused by a low platelet count due to underlying bone marrow failure (aplastic anaemia), rather than due to PNH.

Difficulty swallowing (dysphagia)

When the PNH red blood cells are destroyed, the haemoglobin from the damaged cell is released into the blood plasma. Haemoglobin is not meant to be free within the plasma as it binds to oxygen as well as other gases. Nitric oxide is a gas used by the body to help the smooth muscles of the intestine to work properly. The free haemoglobin causes there to be less nitric oxide and this can lead to spasms in the muscles of the intestinal/digestive system. This can affect the oesophagus (gullet) and cause difficulty swallowing.

Abdominal and back pain

The reduction of nitric oxide caused by the free haemoglobin can also affect the intestines causing abdominal pain. It is also possible that abdominal pain can be caused by a blood clot.

Erectile dysfuction

Approximately half of men who are affected by PNH experience erectile dysfunction. It is understood that this is caused by the reduction of nitric oxide by the free haemoglobin. This symptom is generally worse during an attack of haemoglobinuria.


Fatigue and tiredness are very common symptoms of PNH. PNH patients experience differing levels of fatigue and some are even prevented from doing a very basic level of activity. Fatigue is also a symptom of the reduction of nitric oxide (caused by free haemoglobin) and therefore it can occur even when the haemoglobin levels are normal. Due to the constant destruction of PNH red cells, patients can be chronically fatigued. Chronic anaemia resulting from haemolysis aggravates fatigue. Situations where haemolysis can be worse (infections, pregnancy, strenuous work) can make fatigue worse and affect quality of life.


This is yellow discolouration of the skin and the whites of the eyes (sclera) due to the continuous destruction of red blood cells. When haemoglobin breaks down, billirubin is released. This is yellow in colour and is usually processed by the liver. When the level of haemolysis is high, the liver has difficulties processing the bilirubin quickly enough and this leads to jaundice.

Kidney Damage

PNH patients can suffer from kidney damage to varying degrees. During episodes of severe haemolysis and heamoglobinuria, the kidneys can have difficulty processing the haemoglobin which they are filtering. This can cause sudden and temporary kidney failure. It is important to drink plenty of water during episodes of haemoglobinuria in order to hydrate the kidneys and reduce the risk of acute kidney problems. Kidney problems in PNH can also occur due to blood clots and other treatments which are necessary to treat associated conditions like aplastic anaemia.

Blood clots

These are also known as thromboses and are a common complication of PNH. They occur in up to half of PNH patients. Blood clots can be serious or life threatening and therefore these need to be treated quickly. The symptoms of a blood clot vary greatly and depend on where the clot develops and the extent of the clot. Clots can occur anywhere including unusual places like the veins around the liver and in the brain.



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