Composition and function of the blood

Blood is made in the bone marrow. It is composed of red blood cells, platelets, plasma and white blood cells, collectively referred to as blood components. Donations given at our regular blood donation sessions are referred to as "Whole Blood".

Platelets are very small cells. They work with the clotting factors in plasma to form a mesh "plug" to stop or prevent bleeding.

Plasma is the fluid part of the blood. It contains protein, salts and clotting factors.

White cells fight harmful bacteria and help prevent infection.

Red cells carry oxygen from the lungs to the tissues.

Most platelet donations are given to patients who are unable to make enough platelets in their bone marrow. For example, patients with leukaemia or other cancers may have too few platelets as the result of their disease or treatment.

Also after some major surgery or extensive injury, patients may need platelet transfusions to replace those lost through bleeding. Platelets given by our generous and committed donors are often life-saving and special in that they can help up to 3 adults or even 12 children! What’s more, as platelets can only be stored for a few days, regular and frequent donors are in great demand and that is why we ask our platelet donors to attend at least 8 times per year.

Most platelet donations are given to patients who are unable to make enough platelets in their bone marrow. For example, patients with leukaemia or other cancers may have too few platelets as the result of their disease or treatment.

Also after some major surgery or extensive injury, patients may need platelet transfusions to replace those lost through bleeding. Platelets given by our generous and committed donors are often life-saving and special in that they can help up to 3 adults or even 12 children! What’s more, as platelets can only be stored for a few days, regular and frequent donors are in great demand and that is why we ask our platelet donors to attend at least 8 times per year.

Unfortunately not every one who is a blood donor can give platelets.

• You need to have given blood without any problems such as fainting or bruising.
• There is a lower age limit of 18 as donors need to give whole blood without problems first. There is an upper limit of 55 for the platelet donors. (the procedure puts more of a strain on the circulation than whole blood donation).
• You should not be on aspirin or any of the anti-inflammatory painkillers such as ibuprofen. These drugs stop the platelets working properly.
• Platelet donors are asked to attend regularly - at least 8-10 times per year. We understand some people are unable to do this because of the traveling and time commitment.

We can make some platelets from one normal whole blood donation. Usually platelets from minimum 4 donations of the same blood group are combined to provide one adult dose.

However, platelets can also be collected from donors with high platelet counts using a cell separator machine. This takes the blood and spins it to separate it into red cells, white cells, platelets and plasma. The platelets and some plasma are automatically collected into a bag and the rest of the blood, including the red cells, are returned to the donor.

A single donor can give enough platelets to provide 2-3 adult doses or up to 12 small doses of platelets for babies and young children.

Some patients have a large number of platelet transfusions and may develop antibodies. Then they require platelets from a few closely matched donors. Such platelets can only be collected using a cell separator machine.

Yes, very. All the kit used is sterile and disposable so there is no risk of infection.

The main risks, as with whole blood donation are those associated with insertion of the needle and the risk of fainting.

In addition, in order to prevent the blood clotting inside the machine, a substance called citrate is added to it during the process. Citrate may sometimes cause tingling around the lips and fingers. This soon goes away if the process is slowed or stopped.
we closely matched donors. Such platelets can only be collected using a cell separator machine.

When you arrive for your donation you will register at the reception desk and complete the health questionnaire as normal. We will check you are not anemic, as we do for whole blood donation. Then you will be seen by a nurse or doctor for a further health assessment including pulse and blood pressure checks. We will ask for your consent to contact your GP if more information is necessary.

All information you give is confidential.

If you are suitable, a full explanation of the procedure including possible side effects will be given. If you are happy to proceed then you will be asked to sign a consent to join the panel of platelet donors.

If you are not suitable you should not be alarmed as only a small proportion of our whole Blood donors are suitable for platelet donation.

A cuff is placed around your arm, the skin cleaned and the donation needle inserted. Depending on the type of machine used a needle may be put in both arms. Blood samples are taken at this stage for testing in the same way as whole blood donations. Additional tests carried out for platelet donors are to check your general state of health, in particular, to check your platelet count and to determine your tissue type (so that your platelets can be matched to those of a particular patient if needed).

During the procedure, blood is withdrawn, mixed with anticoagulant to prevent clotting and processed by spinning to separate the platelets. The rest of the blood is returned to you, which is why it is safe for you to donate at a much higher frequency than whole blood (as often as every 2 weeks!).

During the procedure, any white cells that remain in your platelet donation are also removed as these could cause problems in a patient despite being harmless to you.

All the tubing that blood comes into contact with is sterile and disposable. There is, therefore, no risk of 'catching' any infection. Also, during the return of your blood, air detectors ensure that none of the sterile air present in the collection gets passed into your vein. If a detector identifies air, the machine will automatically shut down and can only be restarted when the air has been removed.

While you are donating you will be monitored and cared for by qualified staff supervised by nurses. You can read, chat to the staff or relax and you will be offered refreshments. When the procedure is completed the needle(s) will be removed and a dressing applied to the venepuncture site(s).

Following the donation, which should take approximately 90 minutes, you will be able to take a well earned break in our rest area and enjoy some more refreshment if you wish.

We hope that you will make another appointment and on leaving the blood donor centre, you can return to your normal activities (with the same restrictions that apply after whole blood donation).

If at any stage in the procedure you suffer discomfort and wish to discontinue a donation please inform the staff.

• As with whole blood donation, bruising or fainting can occur
• Each time you donate, 30-40ml of blood is lost for sampling and in the tubing. Your blood will be tested at every visit to make sure you are not anaemic and to check your platelet count.
• To avoid clotting during the donation an anticoagulant is automatically added as your blood flows into the machine. A small proportion of this citrate solution is returned to you and mixed with your own red cells. Although it is immediately neutralised on return to you, occasionally it can cause a tingling sensation around the mouth and fingers, or a metallic taste or feeling of vibration.

Do remember that as a volunteer you may withdraw from the programme at any time if you wish. However if you do find that platelet donation is not for you, we very much hope you will return to donating whole blood.