Blood, blood components and blood products

Most blood collected from donors is processed into:
1 Blood components, such as red cell and platelet concentrates, fresh frozen plasma (FFP) and cryoprecipitate, are prepared from a single donation of blood by simple separation methods such as centrifugation and transfused without further processing.
2 Blood products, such as coagulation factor concentrates and albumin and immunoglobulin solutions, are prepared by complex processes using the plasma from many donors as the starting material. In most circumstances it is preferable to transfuse only the blood component or product required by the patient rather than using whole blood (component therapy). This is the most effective way of using donor blood, which is a scarce resource, and reduces the risk of complications from transfusion of unnecessary components of the blood.

WHOLE BLOOD. The average volume of blood withdrawn is 450 ml, taken into 63 ml of anticoagulant. Blood stored at 4°C has a ‘shelf-life’ of 5 weeks when at least 70% of the transfused red cells should survive normally. Whole blood should be reserved for acute blood loss; packed cells or red cell concentrates plus crystalloid or colloid solutions are acceptable alternatives.

PACKED RED CELLS. 200-250 ml of plasma are removed from whole blood to be frozen as FFP or to be further processed.

RED CELL CONCENTRATES. Virtually allthe plasma is removed and it is replaced by about 100 rnl of an optimal additive solution, such as SAG-M which contains sodium chloride, adenine, glucose and mannitol. The PCV is about 0.65 litre litre'” but the viscosity is low as there are no plasma proteins in the additive solution, and this allows fast administration if necessary.

LEUCOCYTE-DEPLETED RED CELL CONCENTRATES are usually prepared by filtration. They are used in patients who have had recurrent febrile transfusion reactions and to prevent alloimmunization to leucocyte antigens in patients likely to receive repeated transfusions such as patients with thalassaemia major.

WASHED RED CELL CONCENTRATES are preparations of red cells suspended in saline, produced by cell separators to remove all but traces of plasma proteins. They are used in patients who have had severe recurrent urticarial or anaphylactic reactions.

PLATELET CONCENTRATES are prepared either from whole blood by centrifugation or by plateletpheresis of single donors using cell separators. They may be stored for up to 5 days at 22°C. They are used to treat bleeding in patients with severe thrombocytopenia and prophylactically to prevent bleeding in patients with bone marrow failure.

GRANULOCYTE CONCENTRATES are prepared from single donors using cell separators. They are used for patients with severe neutropenia with definite evidence of bacterial infection where antibiotic therapy has failed. They are rarely used now.

FRESH FROZEN PLASMA is prepared by freezing the plasma from 1 unit of blood at O°C within 6 hours of donation. The volume is approximately 200 ml. FFP contains all the coagulation factors present in fresh plasma and is mostly used for replacement of coagulation factors in acquired coagulation factor deficiencies.

CRYOPRECIPITATE is obtained by allowing the frozen plasma from a single donation to thaw at 4-8°C and removing the supernatant. The volume is about 20 ml and it is stored at O°c. It contains factor VIII :C, factor VIII :vWF and fibrinogen. It is no longer used for the treatment of haemophilia A and von Willebrand’s disease because of the greater risk of virus transmission compared to virus-inactivated coagulation factor concentrates.

FACTOR VIII AND IX CONCENTRATES are freeze-dried preparations of specific coagulation factors prepared from large pools of plasma. They are used for treating patients with haemophilia and von Willebrand’s disease. High purity products are prepared using purification procedures involving chromatography columns and either monoclonal antibodies or ion exchanges. Intermediate purity products are prepared by conventional fractionation methods. Solvents, detergents and heat treatment are used for viral inactivation. High purity products should be used in preference to the intermediate purity products because of their greater safety and because they cause less immunosuppression in HIV -seropositive patients with haemophilia.

ALBUMIN. There are two preparations: Human albumin solution (4.5%), previously called plasma protein fraction (PPF), contains 45 g litre-1 albumin and 160 mmol litre-1 sodium. It is produced in 50, 100, 250 and 500 ml bottles.
Human albumin solution 20%, previously called ‘saltpoor’ albumin contains approximately 200 g litre-1 albumin and 130 mrnol litre ” sodium and is produced in 50 and 100 ml bottles.
Human albumin solutions are generally considered to be inappropriate fluids for acute volume replacement or the treatment of shock because they are no more effective in these situations than synthetic colloid solutions such as polygelatins (Gelofusine) or hydroxyethyl starch (Haemaccef). However, albumin solutions are indicated for treatment of acute severe hypoalbuminaemia and as the replacement fluid for plasma exchange. The 20% albumin solution is particularly useful for patients with nephrotic syndrome or liver disease who are fluid overloaded and resistant to diuretics. Albumin solutions should not be used to treat patients with malnutrition or chronic renal or liver disease.

NORMAL IMMUNOGLOBULIN is prepared from normal plasma. It is used in patients with hypogarnrnaglobulinaemia to prevent infections and in patients with immune thrombocytopenia.

SPECIFIC IMMUNOGLOBULINS are obtained from donors with high titres of antibodies. Many preparations are available, such as anti-D, anti-hepatitis B, antivaricella- zoster.

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