Putting blood donation into a spin

The national blood service take around 2 million blood donations a year as they aim to meet the demand of UK hospitals. Despite growing demand, safety is always a priority and John Collings says centrifugation is vital when minimising risk   

THE NATIONAL Blood Service (NBS) is an integral part of the National Health Service (NHS), guaranteeing to deliver blood, blood components, blood products and tissues from their 15 blood centres to anywhere across England and North Wales. UK hospitals require a staggering 2 million donations of blood every year for procedures ranging from surgery to cancer therapy. These donations are collected in over 23,000 blood donation sessions that are organised by the NBS every year.

The core purpose of this organisation is to save and improve patients’ lives. In order to deliver this world-class service, the NBS is building strong relationships with both blood donors and the health care community. As part of this initiative, the NBS merged with UK Transplant and Bio Products Laboratory in 2005 to form NHS Blood and Transplant (NHSBT), an organisation dedicated to maintaining and improving the quality of service delivered to patients. The organisation’s role includes encouraging the public to donate blood, organs and tissue along with optimising the safety and supply of these donations. As part of this, the blood supplied by the NBS undergoes strict screening, testing and processing to ensure it is safe for patient use. Every blood centre in the UK must meet strict licensing requirements from the Medicines and Healthcare Products Regulatory Agency (MHRA) and pass a thorough inspection at least once every two years.

At blood donation sessions, each donor fills in a health check questionnaire which helps to ensure that they are at the lowest possible risk of having any infections that can be transmitted via blood. This is extremely important in helping to provide the safest possible blood for patients as although all donations are tested, there is a window period of approximately three months when any recently acquired infections may not be detected. Three colour coded blood samples are taken from each donor and tested for both blood type and the presence of infections. The red sample is tested for antibodies raised against viruses such as hepatitis B, hepatitis C, HIV and Human T-cell Lymphotrophic Virus (a single-stranded RNA retrovirus that can cause leukaemia), and also for antibodies against bacteria such as the spirochete that causes syphilis (Treponema pallidum). The purple sample is used to determine ABO and Rh blood type, which is of paramount importance because the transfusion of an incorrect blood type can be fatal. Finally, the yellow sample is tested using a relatively new technology, NAT (Nucleic Acid Amplification Technology), which is an extra-sensitive test used to detect the hepatitis C and HIV viruses rather than their antibodies. About a third of donations are tested for cytomegalovirus (CMV), and depending on the donors’ recent travel history, discretionary antibody tests for malaria, Trypanosoma cruzi (T-cruzi), and West Nile virus can also be carried-out. When the tests are complete, the results are entered onto the donor’s individual record. The donated blood is then barcoded for traceability by both the NBS and the hospital that receives the donation.

Donated blood is known as whole blood, but it is much more useful separated

Blood gets shipped to hospitals across the UK and North Wales (image courtesy of the National Blood Service)

into its individual components via centrifugation. Red blood cells are widely used to replace lost blood during surgery and to treat blood disorders such as sickle cell anaemia and thalassaemia, which require regular transfusions. White blood cells are given to patients suffering life-threatening infections whose normal system is unresponsive to antibiotics. Platelets are essential for bone marrow, post-transplant, chemotherapy and leukaemia treatments. Plasma can be kept frozen at minus 30 degrees centigrade for up to 12 months and is used to treat cases of massive blood loss and to reverse anti-coagulant treatment. It contains clotting factors which are needed for patients suffering from conditions such as liver disease, where not enough clotting factors are being produced, or after massive transfusions.

Separating whole blood means that a single donation can save more than one life, making centrifugation a vital processing step. Of the 15 NBS centres, 10 are blood processing centres. All 10 of these use Thermo Scientific centrifuges and associated services (such as the Thermo Scientific Sorvall RC12BP, the Thermo Scientific Sorvall RC3BPplus and the Thermo Scientific Hereaus Cryofuge 6000i). These specially designed centrifuges provide each centre with different throughput capacities but ensure that each donation is subjected to the same process. These centrifuges use the sedimentation principle, so that the liquid is separated out in accordance to density. A variety of protocols can be used to specify the amount of force to be applied to the donation. Increasing the speed or time will increase the total gravitational force, resulting in more rapid and improved separation of the components in the blood bag.

The process is altered in accordance to which blood products are required. All donations are used to make red cells but only a select few are used to make platelets and plasma.  If a donation is being processed into red cells only, the first step is to remove white blood cells using special filters in a process called leucodepletion, which reduces the risk of transfusion reactions. The blood bags are placed directly into large Thermo Scientific centrifuges where they are spun at 3900 – 4200 rpm, exerting a force of up to 4925 times gravity. This high-speed spinning separates the blood into three distinct layers. The plasma rises to the top, the red cells settle at the bottom and platelets along with any remaining white blood cells float in the middle, forming the buffy coat. After centrifugation, the blood bag is squeezed using an optipress, forcing the plasma and red blood cells out into separate new bags. This process is stopped automatically when the machine detects red blood cells or plasma in the incorrect tube. If the donation is being used to make platelets the remaining buffy coat is then further processed and is only leucodepleted at the end of processing.

Blood sample being loaded for testing (image courtesy of the National Blood Service)

Time is a precious commodity when processing blood, making it imperative to process multiple batches of donations within strict deadlines with minimal error and delay. In order to meet these demands, each of the 10 NBS blood centres that process blood has between 8 and 18 centrifuges (the Thermo Scientific Sorvall RC12BP, Sorvall RC3BPplus and Hereaus Cryofuge 6000i), which need to be dependable, easy to use and maximise productivity. Some features are especially useful to blood processing centrifuges, such as the Accumulated Centrifugal Effect (ACE) which ensures that results are reproducible, regardless of rotor loading. All centrifuges used by the NBS have easy operation with one-touch recall of commonly used protocols saving valuable operator time. Furthermore, they are ideal for this regulated environment since they all feature a security key so that only fully-trained, authorised personnel can gain access.

Hospitals have a constant demand for donated blood to treat patients who need medical procedures ranging from cancer treatment to surgery. Every day, UK hospitals require 7,000 donations to be able to successfully treat these patients. The NBS plays a vital role in ensuring that this demand is consistently met, through holding 23,000 donor sessions each year. In 2007, around 2 million donations from 1.3 million donors were tested and processed by the NBS, ensuring that the blood is safe for patient use before being issued to hospitals. Every unit of blood that is received by a patient in England and North Wales has been processed by a Thermo Scientific centrifuge in one of the NBS centres, separating the whole blood into its individual components. Centrifugation therefore plays a pivotal role in making the world healthier, as separating blood into its individual components enables a single donation to save more than one life.

To find out more information about donating blood and to locate your nearest blood donor session, please visit www.blood.co.uk