What is anaemia?
Anaemia is a reduction in the amount of haemoglobin in the blood. Haemoglobin is required to carry oxygen to the organs and muscles, so too little haemoglobin results in a reduction in oxygen supply. Anaemia is common in kidney disease, but many other conditions can also cause anaemia.
Causes of anaemia
There are three main types of cells in the blood:
- Red blood cells – doughnut-shaped cells produced in the bone marrow. They contain haemoglobin (Hb) – a combination of an iron-containing molecule ‘haem’ and the protein ‘globin’. Haemoglobin gives blood its red colour and carries oxygen in the blood and releases it in our organs.
- White blood cells – (also called leucocytes) which help to fight infection.
- Platelets – which contain substances that aid blood clotting and plug holes in our small blood vessels.
A full blood count (FBC) is a laboratory blood test to measure the amount of haemoglobin and the numbers of red cells, white cells and platelets in the blood. It is also used to check the size and haemoglobin content of the red cells.
Common causes of anaemia
Anaemia can occur in many diseases and for many reasons, but common causes include:
- kidney disease
- blood loss
- a shortage of substances needed to make blood: most commonly iron, but also folic acid and vitamin B12
- illnesses that cause inflammation such as rheumatoid arthritis
- diseases of the bone marrow, where blood is made
- kidney disease
Anaemia and kidney disease
Kidneys normally secrete a hormone called erythropoietin (EPO). This controls the production of red blood cells in the bone marrow. In severe kidney disease, anaemia occurs because the kidneys cannot make enough erythropoietin.
- shortness of breath
- feeling tired and lacking energy
- noticeable heartbeats (palpitations)
Anaemia and kidney disease
Mild anaemia can occur in people with stage 3b chronic kidney disease but it usually only becomes a significant problem at stages 4 or 5.
A shortage of erythropoietin is the most important factor, but other causes can contribute to the development of anaemia:
- People on haemodialysis lose small amounts of blood at each treatment.
- Kidney disease reduces the ability of the body to absorb and use iron to make new red blood cells.
- Inflammation and infection can suppress the bone marrow.
Treating anaemia by increasing the amount of haemoglobin in the blood helps to restore energy, improve stamina for exercise, and may help improve other problems, such as problems with sexual function.
Iron concentrations are often low in people with kidney disease either because their diet doesn’t contain enough iron, or there’s something wrong with how the body absorbs iron from the food as it is digested. Extra iron is given (either in the form of iron tablets or intravenous iron injections) to provide enough for normal production of red cells and to reverse or lessen the anaemia.
In the past, blood transfusion was the only really effective treatment for renal anaemia, but it had a number of problems:
- Each transfusion could carry a small risk of infection by viruses (eg cytomegalovirus, Epstein-Barr virus, Hepatitis B and C viruses, HIV) in the blood.
- Some people’s immune systems could mistake the cells in the blood transfusion for an ‘invader’ and react by making antibodies to them. This could result in potential difficulties:
- matching possible future kidney transplants
- matching blood for further transfusions.
- Patients could have allergic reactions during transfusions.
- Repeated transfusions could lead to iron building up in the body, particularly in the heart and liver, causing damage to these organs.
- Blood transfusions appear to reduce the body’s immunity to infection.
Since 1985 when artificially produced erythropoietin (EPO) became available it has been a very successful treatment for renal anaemia. It replaces the erythropoietin that healthy kidneys would be producing and needs to be given by injections every few days or weeks. In people receiving haemodialysis, the injections are usually given into the machine. In people not on any form of dialysis and those on peritoneal dialysis, the injections are normally given under the skin, like insulin.
Anaemia in people with kidney disease often requires a combination of additional iron (either in the form of iron tablets or intravenous iron injections) and EPO injections. EPO speeds up the production of red blood cells in the bone marrow, but this takes time, so, it can take several weeks for treatment to work.
Side effects are rare but some are important, for example:
- High blood pressure, especially if the haemoglobin (Hb) level rises rapidly, or becomes too high
- Clotting of fistulas used for haemodialysis may be more likely if haemoglobin levels are high
- Heart disease and stroke are more common if treatment is adjusted to increase the haemoglobin level towards normal levels
- Very rarely patients react to EPO, making antibodies that stop it working. The bone marrow stops producing red cells, which results in a condition called “pure red cell aplasia”. This is a very severe anaemia that can only be treated with blood transfusions.
The best level for haemoglobin if you have kidney disease is probably low-normal or a little bit lower than normal. This relieves the symptoms of anaemia without causing complications.
- Don’t hesitate to speak to your kidney specialist or renal unit if you think you may have anaemia or need treatment with iron or EPO – or if you need help with any other aspects of your illness.
Help for you
If you have been diagnosed with anaemia and have any questions or concerns about your condition don’t hesitate to speak to your GP.
Reviewed April 2019
Our research improves lives
A major study funded by Kidney Research UK has been investigating the use of intravenous iron to treat anaemia. In results recently published, the trial demonstrated that giving patients on haemodialysis a higher dose of iron reduced the risk of death, hospitalisation for heart failure and other major cardiovascular events.
This is a major step forward and is likely to impact how haemodialysis patients are cared for across the world.
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