Blood products

 

As previously unrecognised or unmanageable medical conditions have been diagnosed or become treatable, so the need for new medical procedures and products, including those derived from blood, has expanded. Fortunately, the response by researchers to these increasing demands has been positive, with technological advances allowing for the development of products that utilise blood more efficiently than before, and which are clinically better suited than their predecessors for the functions that they are called upon to perform. Although the number of blood products and derivatives is constantly changing, they can be said to fall into four general categories of product.

i) Whole blood products

When blood transfusion was in its infancy, the standard procedure for treating patients in need of blood involved the transfusion of whole blood, whereby the full, unmodified contents of a blood donation would be transfused into the recipient. In recent decades, improvements in blood collection and processing have meant that medical practitioners have been able to shift away from providing whole blood transfusions in favour of giving only those particular blood components required by patients. The result has been a significant reduction in the clinical use of whole blood – for example, while in 1975 over 90 percent of all blood donations collected in the UK were transfused as whole blood, by the end of the twentieth century, the corresponding figure had fallen to less than 5 percent of the total collected [1]. Nevertheless, while largely superseded in general use, whole blood continues to be retained as a treatment option following cases of massive blood loss, as occurs with cardiac surgery on infants, following haemorrhaging incurred during childbirth or as a result of the infliction of a serious wound.

ii) Plasma derivatives

As was previously noted, plasma is the fluid that transports cellular components and associated substances to their intended destinations. When the level of plasma in the blood stream is sub-optimal, blood becomes thicker and the speed of circulation slows down, resulting in, amongst other things, body tissue being starved of the oxygen carried by the red cells or immune system weakness due to limited white cell activity. By receiving plasma infusions, a recipients’ blood level is diluted by an increased volume of fluid, allowing for circulation to function at a normal speed once again.

The basic plasma product is fresh frozen plasma (FFP), which is obtained by separating plasma from the other components of a unit of whole blood. Although it can be derived from whole blood that has reached its expiry date, the standard way of obtaining plasma is via a process known as plasmapheresis. Here, a donor is connected to a machine known as a blood cell separator, which extracts a set quantity of whole blood from the donor’s body. This whole blood is then spun around in a sterile centrifuge, with the different blood components being naturally separated into different layers that depend upon their respective densities. The topmost, least dense layer is constituted mainly of plasma, which is retained by the machine, while the remaining fluid, composed mainly of the denser cellular components, is pumped back into the body of the donor. Thereafter, the collected plasma is pooled with the plasma obtained from other plasma donors, where, in order to retain its best features, it is frozen as soon as possible (hence its name). Of all the products that can be obtained from blood, fresh frozen plasma has one of the longest life spans, as it can be safely stored without any major deterioration in its properties for up to one year after donation.  

While FFP can be utilized for medical applications, it is sometimes subject to misuse, as the indications for its proper utilisation are not always clearly specified. Rather, it is commonly used in the preparation of cryoprecipitate, which is the basic raw material used to produce a wide range of specialised plasma products. Probably the best known of these medical treatments is factor VIII concentrate, which is the product of choice for people suffering from haemophilia A (or factor VIII deficiency). This product is supplied as a freeze-dried powder that must be reconstituted with sterile water before the recipient can consume it via intravenous injection. As it has a relatively short half-life of only 12 hours, regular doses need to be taken by the recipient if this product is to have a sustained effect. Although factor VIII concentrate is by far the most important cryoprecipitate derived product, there are other products on offer as well. For example, factor IX concentrate is utilised by patients with haemophilia B, factor XI is occasionally administered to people suffering from thrombosis or cardiovascular disease, while factor VII concentrate may be used to control the serious haemorrhaging that can result from advanced liver disease or from an overdose of oral anticoagulants [2].

In addition to cryoprecipitate, FFP is also used to produce cryosupernatant, which is used in the preparation of a different series of plasma-based products. Amongst these products are immunoglobin extracts, which are used in the preparation of short-term prophylaxis against various diseases. These extracts are generally obtained from donors whose plasma contain high antibody levels to particular diseases, either as a result of a previous infection by the relevant virus, or due to exposure in an immunization programme [3]. In addition, we have human albumin solution, which was first developed in the USA during the Second World War to treat military casualties in combat zones, where the availability of blood supplies was limited. The technique of extracting albumin involves the fractionation of pure albumin from pooled plasma that has been treated with ethanol. The resulting product is then sterilized by filtration and pasteurisation at 60° C for 10 hours, whereupon it is then bottled and inspected for contamination for at least 2 weeks before being released for use [4]. Due to its highly concentrated nature [5], albumin has been used to treat people who have suffered significant plasma loss following severe burns, as well as amongst intensive care patients, although its true worth as a medical tool has been questioned on a number of counts [6].

iii) Red cell products

In many instances, when the term “blood transfusion” is used, what is actually being referred to is the transfusion of red cells, as red cell products have largely taken up many of the roles for which whole blood transfusions were originally used. This confusion is understandable though, since many of the factors that characterise blood, such as haemoglobin and the blood groups, are largely defined by the red cells.

In the 1960s, red blood cell products had a useful lifespan of only 21 days, but with advances in preservation technology, they can now be safely used up to 35 days after donation (with some test products showing signs of validity for periods of 42 days). While red cells are frequently acquired from donated whole blood, they can, like plasma, be extracted from a cell separator machine via a process known as cytapheresis [7]. Although red cells are essentially used to transport oxygen to tissue, they are processed into different products that can be utilized to treat a variety of ailments. Some of the more common products are whole red cells (which are basically red cells obtained once plasma has been removed from whole blood); red cells in additive solution (red cells placed in a protective shell to permit maximum plasma retrieval); frozen red cells (which are available for use in patients with rare blood types, where finding suitable donors within the necessary time may be difficult) [8]; and leukocyte depleted red cells (which are subjected to a special filtration process that removes virtually all white cells from the final product).

iv) Platelet based products

Products derived from platelets are generally used to treat incidents of bleeding, which arise during surgery or due to illnesses such as cancer and leukaemia (a disorder caused by bone marrow failure), where their clotting properties are able to prevent massive blood loss. As platelets have an intermediate density in whole blood, special measures must be taken to collect them, with two main techniques being commonly used. The first approach involves multiple apheresis, whereby donated blood is spun several times in order to progressively eliminate non-desirable blood components from being collected until only the required layer of platelets (known as the buffy coat) is retained. The alternative method involves the use of a slightly different machine that automatically separates blood into its various components without recourse to a centrifuge, with rejected components being returned immediately to the donor [9]. The main disadvantage of platelet products is their relatively short shelf life, as they have to be used within about 5 days of donation before their most vital properties are lost.