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Plasma is the fluid part of blood and makes up the bulk of the volume. It contains substances that can be used to treat a number of different conditions.
Blood is made up of four separate components, which each perform a different function. They are:
- red blood cells – carry oxygen around the body and remove carbon dioxide
- white blood cells – help the body fight infection
- platelets – tiny cells that trigger the process that causes the blood to clot (thicken)
- plasma – yellow fluid that transports blood cells and platelets around the body and contains a number of substances, including proteins
What is plasma?
Plasma is the largest component of blood, making up about 55% of its overall content. It's mainly made of water and surrounds the blood cells, carrying them around the body.
Plasma helps maintain blood pressure and regulates body temperature. It contains a complex mix of substances used by the body to perform important functions.
These substances include minerals, salts, hormones and proteins.
Three important proteins found in plasma are:
- clotting (coagulation) factors
How plasma components are used
Plasma components can be used in a number of different ways, depending on the condition they're being used to treat.
The two main methods of using plasma are:
- fresh frozen plasma transfusion – where plasma is separated from donated blood and frozen until needed; it's then thawed under controlled conditions and transfused to the recipient
- plasma exchange – where a special machine is used to remove plasma from the patient's blood; it's then replaced with a substitute plasma component from donors
Read more about how plasma and plasma components are used.
The following plasma components can be used to treat a variety of different conditions.
Albumin cleans the blood, carries substances around the body, and helps maintain the correct amount of fluid circulating in the body.
Human albumin solution can be used as a treatment to help people with severe burns, sepsis, liver disease or kidney disease.
Clotting (coagulation) substances called clotting factors help control bleeding and work together with platelets to ensure the blood clots effectively.
Fresh frozen plasma and clotting factors can be used to treat bleeding disorders. For example, they can be used in severe injuries when there's a lot of bleeding.
In the UK, specific clotting factors are also used to treat haemophilia, an inherited condition that affects the blood's ability to clot.
Immunoglobulins are part of the immune system (the body's natural defence against infection and illness).
Immunoglobulins are antibodies that the body produces to fight a variety of infections. For example, they're used to fight health conditions such as:
- chickenpox – a serious but usually shortlived viral infection
- hepatitis – a viral infection that causes the liver to become inflamed (swollen)
- rabies – a very rare infection of the central nervous system that's passed on to humans from infected animals
Normal human immunoglobulins can be used to support people who have conditions where their immune system is having difficulty producing antibodies.
Plasma is the source of anti-D immunoglobulin, a substance often given by injection to pregnant women with a rhesus-negative blood group (RhD negative) whose unborn baby may have a rhesus-positive blood group (RhD positive).
This treatment prevents the mother becoming sensitised to the baby's blood and stops immune anti-D developing. Immune anti-D can cause rhesus disease in subsequent pregnancies, which is a potentially fatal condition.
Risks of using plasma components
Some people can experience problems related to a plasma transfusion.
These can vary in severity from a slight increase in temperature to the development of a serious condition called variant Creutzfeldt-Jakob disease (vCJD) in very rare cases.
Read more about adverse reactions to plasma components.
Plasma and plasma products can be removed from blood in a number of different ways, allowing them to be used to treat a variety of conditions.
The main ways that plasma is used include:
- plasma transfusions
- plasma exchange (plasmapheresis)
Plasma products can be used to help prevent health problems occurring in conditions such as rhesus disease (where antibodies in a pregnant woman's blood destroy her baby's blood cells).
They can also be used to prevent bleeding in people who have haemophilia (an inherited condition that affects the blood's ability to clot).
Fresh frozen plasma
To obtain plasma for transfusion, a donation containing all the components of blood (whole blood), including plasma, is taken from one person.
The plasma is then separated from the red cells and frozen, becoming fresh frozen plasma. When needed, it is thawed and given as a transfusion to another person.
For example, a patient may be given a plasma transfusion if they are bleeding after a serious accident or following major surgery, where clotting factors need to be replaced in addition to red blood cells.
Before someone is able to donate blood for transfusion, they have to comply with a strict set of guidelines about their medical, travel and sexual history. This ensures it is safe for them to donate and that their blood is safe to be transfused.
As with red blood cells, plasma is always checked for viruses to make sure it is as safe as possible to use.
Most people receiving plasma receive fresh frozen plasma. This is stored frozen at -25C for up to three years, so it needs to be carefully thawed before use.
Pathogen-inactivated fresh frozen plasma
Plasma transfused to patients born after January 1 1996 comes from donors outside the UK to reduce the risk of variant Creutzfeldt-Jakob disease (vCJD) a rare and fatal brain condition.
There are two products available. One is produced by UK blood services and has been treated with a chemical called methylene blue (an additional step to make plasma safer). The alternative is a batched, mixed plasma called Octaplas that has been treated with solvent detergent to make it safer.
Cryoprecipitate is plasma that has been specially treated so that it is rich in certain proteins, including fibrinogen (a special protein that helps blood to clot).
Read more about blood transfusions for more information about the process.
Plasma products made by fractionation
Many of the components found in plasma can be separated and removed so they can be used to treat specific problems.
Some plasma donations are mixed (pooled) and are then subjected to a number of different heat and chemical treatments.The various proteins are then separated out in a complex process known as fractionation.
All blood donations used to make plasma pools for fractionation have to be checked for viruses to make sure they are as safe as possible to use. The pooled plasma is also carefully filtered and "cleaned" using heat, detergents and solvents to remove any viruses that may be present.
After the fractionation process has been completed, the plasma products are either kept as a liquid or freeze-dried as a powder for reconstitution before use. They are then packaged, ready for distribution to clinics, surgeries and hospitals.
There are numerous plasma products, but the three main ones are:
- human albumin solution
- clotting (coagulation) factors
- normal human immunoglobulin
See above for more information about these.
Plasma exchange, also known as plasmapheresis, is a procedure where a machine called a cell separator is used to separate plasma from the other components of a person's blood.
During the procedure, the plasma is removed and replaced with a substitute (usually human albumin solution) and the red cells, white cells and platelets are returned to the patient.
Plasma exchange is often used to treat rare blood conditions. Some of these are briefly outlined below.
Thrombotic thrombocytopenic purpura
Thrombotic thrombocytopenic purpura is a rare clotting disorder affecting the platelets, where microscopic blood clots form and damage organs and red blood cells.
Plasma exchange separates and removes the plasma from the rest of the blood and replaces it with solvent detergent plasma. This replenishes levels of a vital enzyme that controls the platelet clotting and removes the antibodies responsible for the condition.
Multiple myeloma and Waldenström's macroglobulinaemia
Multiple myeloma and Waldenström's macroglobulinaemia are both rare types of bone marrow cancer where abnormal bone marrow cells create large amounts of a protein called a paraprotein (immunoglobulin).
If the protein levels in the blood become too high, the blood can thicken, which is known as hyperviscosity. The symptoms of hyperviscosity include:
- fatigue (tiredness)
- blurred vision
Plasma exchange reduces the amount of abnormal protein in the blood, which helps relieve the symptoms. However, the process does not prevent the production of immunoglobulin. Other treatments, such as chemotherapy, may be required to achieve this.
Plasma exchange procedure
During plasma exchange, a machine called a cell separator is used to separate the plasma from the rest of the blood. A needle is inserted into a vein in the arm and the blood is removed and passed through the cell separator.
The plasma is separated from the rest of your blood and a plasma substitute is added before the blood is returned through a needle in a vein in the other arm.
Plasma exchange takes about two hours to perform. During the process, only a small amount of blood (less than 100ml) will be outside the body at any one time. This is because the blood is being removed and returned at the same rate.
The amount of plasma exchanged will depend on factors such as:
- your height
- your weight
- how viscous (thick) your blood is
The number of plasma exchanges needed will depend on your symptoms and how well you are responding to your other treatments.
Faintness and lightheadedness are both possible side effects of a plasma exchange. If you feel faint or lightheaded, you should tell the healthcare professional treating you.
The symptoms can usually be effectively treated by changing to a lying down position. Ensuring you have something to eat on the day of the procedure will also help prevent these symptoms.
During a plasma exchange, you may also experience numbness or a tingling sensation around your nose and mouth and in your fingers. This is caused by a substance called citrate, which is added to your blood as it goes through the machine to prevent it clotting. The citrate may affect the levels of calcium in your blood.
Let the healthcare professional treating you know if you experience numbness or tingling sensations. They may stop the plasma exchange for a few minutes until your body adjusts to the increased citrate levels in your blood, or they may increase the level of calcium in your blood.
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Plasma components can save lives, but their use isn't without risk. In some cases there can be adverse reactions, which can differ in severity.
Adverse reactions that you could experience after having a plasma transfusion include:
- a slight rise in temperature
- itching and sometimes a rash (hives) – this can occur within a few minutes of starting a plasma transfusion, but can usually be cured by slowing down the rate of transfusion or by taking an antihistamine (medication to treat mild allergic reactions)
- anaphylaxis – a rare but life-threatening allergic reaction
The risk of developing an infection after receiving plasma is very small. All blood donations used to make plasma are carefully screened for viruses to make sure they're safe.
However, as is the case with most medical procedures, there are possible risks associated with receiving plasma. Some of these are outlined below.
Transfusion-related acute lung injury (TRALI)
Transfusion-related acute lung injury (TRALI) is a reaction that can occasionally occur in someone who receives a plasma transfusion. During or shortly after the transfusion the person will have breathing difficulties, which can sometimes be severe.
The reaction is thought to occur because the donated plasma contains antibodies (proteins produced by the donor's immune system), called HLA antibodies, that react with your white blood cells.
This occurs more often when plasma has been donated by a female donor who's had pregnancies in the past and whose immune system produced the antibodies as a response to pregnancy.
Antibodies are usually produced by the immune system to fight organisms in the blood that the body regards as "foreign", such as bacteria. However, in pregnancy they have a protective role.
To minimise the risk of TRALI, plasma from male donors is usually used to make fresh frozen plasma and other plasma-containing blood components and products used for transfusion.
Fractionated plasma products don't cause TRALI.
Variant Creutzfeldt-Jakob disease (vCJD)
Variant Creutzfeldt-Jakob disease (vCJD) is the human form of bovine spongiform encephalopathy (BSE), commonly known as mad cow disease.
First identified in 1996, vCJD is a rare neurological illness that causes brain damage. It occurs as a result of eating the meat of cattle infected with BSE.
The risk of developing vCJD after having a blood transfusion is very small, but there's currently no test available to screen donated blood for the prion protein that causes vCJD.
Each year in the UK, over 2 million units of blood are transfused. To date, there have only been a few cases where patients are known to have become infected with vCJD after having a blood transfusion.
However, to minimise the risk further, the NHS has put a number of precautions in place. These include:
- removing all white cells by filtering cellular blood components (red blood cells and platelets)
- importing fresh frozen plasma from countries where there have been no cases of vCJD for transfusion to those born on or after January 1 1996
- using pooled plasma for fractionation from countries where there have been no cases of vCJD, and using recombinant clotting factors (produced in a laboratory using DNA technology) for treating people with haemophilia, where these products are available
- only using plasma transfusions when absolutely necessary
Read more about Creutzfeldt-Jakob disease (CJD).
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