Blood is a raw material from which different therapeutic products are made. These are blood components (red cell concentrates, platelet concentrates, fresh plasma and cryoprecipitate) and plasma derivatives (albumin, coagulation factors and immunoglobulins).
This section summarises the preparation of the different blood products and the steps that are taken to make them safe and effective. Figure 2 illustrates the steps in processing of blood from the donor to the patient.
Figure 2 - Production of blood components and plasma derivatives
[Figure 2 resources: View large format, download as gif, pdf or Word™ document]
The medical selection of donors is intended to exclude anyone whose blood might harm the recipient, for example by transmitting infection, or anyone who might possibly be harmed by donating blood. Donors can give 450−500 ml whole blood, generally up to three times per year. Platelets, plasma and red cells can be prepared from whole blood donations or collected by a process called apheresis (or component donation).
Blood component therapy
During the 1980s, the production of factor VIII (antihaemophilic factor) by plasma fractionation was established in the UK. There was a large demand for factor VIII for haemophilia treatment, and the blood services obtained plasma for fractionation by separating it from whole blood donations. This stimulated the introduction of the use of blood component therapy, in which patients are transfused with red cells, plasma or platelets rather than with whole blood. However, after removing the plasma from a unit of donated whole blood, the concentrated (packed) red cells remain as a viscous fluid that is difficult to infuse. Furthermore, the glucose and adenine red cell nutrients are removed so that conditions for red cell storage are not optimal. For these reasons, current practice is to remove all but a few millilitres of the plasma and replace it with a red cell additive solution specifically formulated to support red cell metabolism during storage.
Routine tests on blood donations
All donations are tested for hepatitis B (surface antigen), HIV (antibody), HTLV (antibody), hepatitis C (antibody and RNA), and syphilis (antibody). Tests for malaria antibodies, T. cruzi antibodies or West Nile virus RNA may be used when travel may have exposed a donor to risk of these infections. Some donations are tested for cytomegalovirus antibody to meet the needs of specific patient groups (see Prevention of cytomegalovirus transmission). The epidemiology of infections in the population and among donors is monitored in order to inform future testing strategies for further risk reduction.
Blood groups and blood group antibodies
Each donation is tested to determine the ABO and RhD group of the donor’s red cells. Group O donors are also tested by the blood services to detect those donations that contain high levels (titres) of anti A or anti B antibody.
Manufacture of plasma derivatives
Plasma derivatives are partially purified therapeutic preparations of human plasma proteins that are manufactured in a pharmaceutical process from large volumes of plasma, typically from at least 20,000 individual donations, i.e. about 5,000 kg of plasma. Controlled thawing, addition of ethanol and exposure to varying temperature, pH and ionic strength are combined with filtration, chromatography and centrifugation to separate different groups of proteins. Further purification and virus inactivation steps are carried out. The final products are supplied as solutions or freeze-dried powders. All plasma derivatives licensed in the UK are treated to inactivate viruses. To avoid possible risks of vCJD, since 1999 the UK has imported plasma for fractionation from areas reporting a low incidence of BSE.
Blood component labels
The label content is prescribed by the Blood Safety and Quality Regulations 2005 (BSQR). Bar-coded information allows the origins and processing steps of the product to be traced (Figure 3).
Blood components supplied for an individual patient must have a label that is attached to the pack by the hospital blood bank. This label must carry information that uniquely identifies the patient for whom the component has been selected, and may also be designed in order to record the final fate of the component. An essential check before infusing any blood component is to make sure that the details on this compatibility label match exactly with the identity of the patient recorded on the wristband.
Plasma derivative labels
These are licensed pharmaceutical products. The labelling and other information supplied with each vial is specified by the regulatory authority.