Box 145 Whole blood

Whole blood is blood that has been aseptically withdrawn from humans. A suitable anticoagulant is added (often heparin or a citrate-dextrose-based substance), although no preservative is present. The blood is usually stored at temperatures ranging from 1-8 °C, and has a short shelf life (48 h after collection if heparin is used as the anticoagulant, or up to 35 days if citrate-phosphate-dextrose with adenine is employed).

The blood is generally warmed to 37 °C immediately prior to transfusion. Whole blood is often used to replace blood lost due to injury or surgery. The number of units (one unit equals approximately 510 ml) administered depends upon the health and age of the recipient, along with the therapeutic indication. Administration of whole blood may also be undertaken to supply a recipient with a particular blood constituent (e.g. a clotting factor, immunoglobulin, platelets or red blood cells). However, this practice is minimized, in favour of direct administration of the specific blood constituent needed.

Associated with the administration of blood or blood products is the risk of accidental transmission of infectious agents such as hepatitis viruses or HIV. The prevention of accidental pathogen transmission relies upon:

• careful screening of all blood donors/donations;

• introduction of methods of pathogen removal/inactivation during the processing steps;

• careful screening of all finished products.

The identity of each blood donor should be recorded, and all donor blood bags must be labelled carefully. Traceability of individual blood donors/donations is essential, in case the donor or product is subsequently found to harbour blood-borne pathogens. The risk of contamination of blood during collection/processing is minimized by using closed systems and strict aseptic technique.

Before any blood donation is released for issue/processing, it must be tested for the presence of various pathogens particularly likely to be present in blood. In most countries, these tests include immunoassays capable of detecting:

• hepatitis B surface antigen (HBsAg);

• antibodies to hepatitis C virus;

• syphilis antibodies.

However, no immunoassay is 100 per cent accurate and all will report a low number of false negatives (and false positives). It is believed that in the order of 1 in every 42 000 blood units reported to be HIV antibody-negative actually harbours the virus.

In general, processes capable of inactivating viral or other pathogens (e.g. heat or chemical treatment) may not be applied to whole blood or most blood-derived products. Thus, for whole blood at least, effective screening of donations is relied exclusively upon to prevent pathogen transmission. Many of the processing techniques used to derive blood products from whole blood (e.g. precipitation, but especially chromatographic purification) can be effective in separating viral or other pathogens from the final product (see also Chapters 6 and 7). Fractionated products, therefore, are less likely to harbour undetected pathogens.

In addition to being screened for likely pathogens, the ABO blood group and the Rh group is also determined. In the USA alone, in the region of 35 transfusion-related deaths occur annually due to errors in blood group typing or the presence of bacteria in the product.

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