The Institute of Biomedical Science

Blood, blood transfusion and the role of biomedical scientists

Transfusion science

The blood transfusion laboratory provides blood and blood products to patients of road traffic accidents, those with acute blood loss, anaemia, clotting problems and also supports leukaemia cases during chemo- and radiotherapy. Biomedical scientists in the transfusion service are concerned with the identification of individual blood groups and compatibility tests of donors' blood with that of the patient.

They are also involved in specialised testing for resolution of grouping problems; the preparation of rare blood and tissue matched blood products and the preparation of blood components and plasma.

Blood transfusion and the role of biomedical scientists
Each year in the UK some 3 million blood components are transfused to patients, and each of these will have had some degree of testing or processing performed on them prior to issue by biomedical scientists (BMS) operating within blood transfusion laboratories. This short guide therefore highlights their sometimes-unknown role and also answers some of the most commonly asked questions from the public regarding blood and its uses.

What are the duties of a BMS working in transfusion?
Their role is to ensure that any patient who requires a blood transfusion receives a safe transfusion. They test the patient's blood sample, firstly determining their blood group, and then perform laboratory tests with the sample against samples of donated blood given by donors to detect if there are any red cell antibodies present in the patient which may cause problems upon transfusion of the donated blood. Only when they are completely satisfied that the blood is safe do they issue it for transfusion to the patient.

Why do patient's need transfusions in the first place?
Basically, two reasons, either to replace blood lost during surgery or accidents, and also to treat anaemia and other haematological disorders. Surprisingly to most people, the majority of the blood supplied for transfusion is usually planned and ordered days or even weeks in advance, only a small proportion, around 8%, of blood is issued under emergency situations. Surgical procedures account for most transfusions, which uses in the region of 70% of the available blood supply.

What is blood composed of?
Basically blood can be divided into 4 components, red cells, white cells, platelets and plasma. Red cells as stated above are given in surgical and medical situations, white cells however are now removed from donated blood as a safety precaution. Platelets are very useful in combating bleeding disorders and can be harvested and given separately to patients in the form of platelet transfusions. Plasma also is useful to prevent bleeding as it contains clotting factors, and provided the plasma is separated shortly after donation and quickly frozen at very low temperatures, the clotting factors can be usefully preserved, this product is known as 'fresh frozen plasma'.

Is blood dangerous?
The UK has one of the cleanest, safest blood supplies in the world. All our blood donors are unpaid volunteers, who are carefully questioned about their medical health and lifestyles prior to donation. All donated units are then individually screened and tested for amongst other things viruses such as HIV, and hepatitis. Because of these stringent testing procedures it is highly unlikely that hepatitis or HIV could be transmitted via a blood transfusion. The chance of contracting HIV from a UK blood transfusion for instance has been calculated recently as less than one in 2 million, which is about the same risk as that of being struck by lightning.

What About vCJD?
Although there is still no evidence that vCJD has ever been transmitted from human to human by blood transfusions, the risk of this occurring is now regarded as highly possible. The National Blood Service (NBS) therefore take this risk very seriously and so as a precautionary measure, all UK blood donations now have their white blood cells removed by filtration to prevent any possible transmissions of vCJD, as this is the most likely route of transmission. This white cell removal process is known as "leucodepletion". As a further precaution, as of April 2004, new blood donor restrictions were introduced. From that date onwards, anyone who has received a blood transfusion since January 1980 are asked to no longer donate themselves.

How long does blood keep?
Provided the blood is stored correctly under strictly controlled refrigeration, it has a 'shelf-life' of 35 days following donation. If a unit of blood still has not been used within this 35-day period, it is deemed to have expired, and must then be discarded. Transfusion scientists however do their utmost to ensure that every unit of donated blood is transfused prior to expiry. This keeps wastage to an absolute minimum, as not only is blood a costly product to collect and prepare due to the various safety testing precautions involved, it is also often in short supply and must therefore always be used conservatively.

What happens if a patient refuses to have blood?
First of all, a doctor would not prescribe a blood transfusion for a patient in the first instance unless it was absolutely necessary for their continued well being. However, a small proportion of patients sometimes do refuse their blood transfusions, and in these cases, other forms of treatment may be offered if appropriate. New procedures such as 'cell salvage' for instance now allows the patient's own blood to be re-cycled during certain operations which can in some cases remove the need for any donated blood to be transfused at all, and 'autologous transfusions' whereby the patient receives back their own pre-donated blood are both useful alternatives in these cases.

Are some blood groups rarer than others are?
There are 8 major blood groups, A Positive, A Negative, O Positive, O Negative, B Positive, B Negative, AB Positive, AB Negative. The incidence of blood groups can vary from country to country depending on ethnic mix but the approximate distributions in the UK are:

A Positive - 36%
A Negative - 7%
O Positive - 38%
O Negative - 7%
B Positive - 8%
B Negative - 1%
AB Negative - 1%
AB Positive - 2%

How can I find out what my blood group is?
The best possible way to find out is by becoming a blood donor yourself. Anyone can do it, providing they are in reasonable good health, and the minimum age has recently been lowered to 17 to hopefully encourage more young people to donate. . If you are interested in becoming a blood donor, look in your local Telephone directory for the number of your Regional Transfusion Centre, or ring 0845 7 711 711, you will then be given more information on the next donation sessions in your area. Alternatively, more background information on the National Blood Service and blood donors can be found at their website on www.blood.co.uk.

Barry Hill,
IBMS Transfusion Science Advisory Panel
January 2006