Blood Banking

Donating Blood

Who can donate blood?
Blood donors are volunteers who are providing a greatly needed service. About 4 million patients receive blood transfusions each year, and approximately 9,000 units of red blood cells are needed every day. Although 14 million blood units are donated a year, more volunteers are needed to keep the blood supply at an adequate volume.

Donors must meet certain criteria to ensure their safety and the safety of the recipients. These are available on the NBS website

Donors must be:

• 17-59 years of age
• in good health
• weigh at least 50 Kg (7st 12lb), and
• pass a physical and health history examination prior to donation

The physical examination includes measurement of weight, blood pressure, pulse, and temperature as well as a test for anaemia, which requires just a few drops of blood from your finger.

To protect the health of both the donor and the recipient, the health history questionnaire asks about potential exposure to transfusion-transmissible diseases, such as viruses like HIV, hepatitis B and C, as well as parasites that cause diseases such as malaria.

Certain people are not permitted to donate blood for health concerns. This includes:

• Anyone who has ever injected or been injected illegal or body-building drugs
• Men who have had sexual contact with other men
• Patients with haemophilia
• Anyone with a positive test for HIV, or anyone who thinks they might be HIV positive
• Men and women who have engaged in sex for money or drugs
• Anyone who has had hepatitis B or C virus
• Anyone who has had a previous blood transfusion
• Anyone who has had acupuncture, body piercing or a tattoo in the last 12 months
• Anyone who has two family members with Crueutzfeldt-Jakob disease (CJD)

There also may be some restrictions if you are taking certain medications at the time of donation. You may be ineligible to donate or deferred for a period of time. There are also varying deferral periods if you have been vaccinated recently. For a more details visit the NBS website.

Donors have a personal responsibility to help ensure the safety of the blood supply. You should express any concerns or questions you may have about past illnesses you had or may have been exposed to before donating. Who knows, it is possible that maybe someone close to you will be the recipient of your blood donation.

Where can blood be donated?
Blood can be donated at blood transfusion centres, or mobile sites temporarily set up in public areas like colleges, workplaces, and churches. There are hundreds of institutions involved in blood banking throughout the UK.

For more information on where you can go to donate or receive blood, visit the NHSBT website.

What is donated and how often?
Usually one unit of 475mL (just under a pint) of blood is collected into a blood bag from a vein in the inner part of the elbow joint using a new, sterile needle. Your body replenishes the fluid lost during donation in 24 hours, but it may take up to 2 months to replace the lost red blood cells. Therefore blood can usually be donated only once every 16 weeks.

What are the components of blood?
Blood is made up of several components. These components can be separated in the laboratory so that they can be transfused into multiple patients, each with different needs, since rarely will a person need all of the components within whole blood. These components include:

• Red blood cells – main cellular element in the blood; carry oxygen to the body tissues; used in the treatment of anaemia resulting from, for example, kidney failure, gastrointestinal bleeding, or blood loss during trauma or surgery 
• Platelets – cellular elements needed for blood to clot; used in the treatment of leukaemia and other types of cancer and conditions in which patients have a shortage of platelets (e.g., thrombocytopenia) or abnormal platelet function to control bleeding 
• Plasma – straw-coloured fluid part of blood in which the red and white blood cells and platelets are suspended; helps to maintain blood pressure and the fluid-electrolyte and acid-base balances of the body and transport wastes; used to help control bleeding when no coagulation factor-specific concentrate is available 
• Cryoprecipitate – is prepared from plasma and contains fibrinogen
• White blood cells – cellular elements that fight infection and function in the immune process, one type, called granulocytes, can be transfused to fight infections that are unresponsive to antibiotic therapy, although the effectiveness of this form of treatment is still being investigated

Separation of these components is performed by first treating the blood to prevent clotting and then letting the blood stand. Red blood cells settle to the bottom, while plasma migrates to the top. Using a centrifuge to spin out these components can speed up the process. The plasma is then removed and placed in a sterile bag. It can be used to prepare platelets, plasma, and cryoprecipitate, again with the help of a centrifuge to separate out the platelets. Plasma may be pooled with that from other donors and processed further (fractionated) to provide purified plasma proteins, such as albumin, immunoglobulin, and clotting factor concentrates.

Protecting the Blood Supply

Testing Donated Blood
In the blood bank laboratory, certain tests must be performed on all donated blood. This includes typing to determine the donor’s ABO blood group and Rh status as well as several screens to ensure the safety of the blood. Screening is conducted for 1) unexpected red blood cell antibodies that could cause reactions in the recipient (such as those made as a result of a previous transfusion or pregnancy) and 2) current and past transmissible infections; each unit of donated blood is tested for:

• Hepatitis B 
• Hepatitis C 
• HIV types 1 and 2 
• Syphilis

Testing for these infectious diseases often is done by antibody screening, such as the HIV antibody test, which looks for the antibodies the body makes in response to the invading virus.

Confirmatory tests also are performed if any test results are positive in order to rule out false positives. Once the testing is completed, those units of blood that are free of infection are made available for transfusion when needed. Those in which infection is detected are discarded, and the donor is notified as well as prohibited from future blood donation.

It also is important to realise that there are some infectious diseases that are not or cannot be tested for at the present time, such as the West Nile virus. The potential for an infectious agent that will not be detected in testing to be present in a donated unit underscores the importance of donors reporting any transmissible infections they have had or may have been exposed to in the past.

Storing Blood Safely
Proper storage of whole blood and blood components is essential.

• Red blood cells must be stored under refrigeration and can be kept for a maximum of 42 days or frozen for up to 10 years. 
• Platelets can be stored at room temperature for a maximum of 5 days. 
• Fresh frozen plasma can be kept frozen for up to 1 year. 
• Cryoprecipitate made from fresh frozen plasma can be stored frozen for up to 1 year. 
• Granulocytes (white blood cells) must be transfused within 24 hours of donation.

Ensuring Proper Use

Blood Typing
Blood typing involves testing a person’s blood for the presence or absence of certain antigens that are present on the red blood cells. Two of these antigens, or surface identifiers, are the A and B markers included in ABO typing. People whose red blood cells have A antigens are considered to be blood type A; those with B antigens are type B; those with both A and B antigens are type AB; and those who do not have either of these makers are considered to have blood type O, which is the most common. Our bodies produce antibodies against those ABO antigens we do not have on our red blood cells, which is why we can receive blood only from donors with certain blood types.

Another important surface antigen is called Rh factor. If it is present on your red blood cells, your blood is Rh+ (positive); if it is absent, your blood is Rh- (negative).

ABO and Rh blood typing are conducted on all donor units by the collection facility and in the laboratory for hospital patients. There are two steps to ABO typing: forward and reverse typing. First, forward typing is performed by mixing a sample of blood with anti-A serum (serum that contains antibodies against type A blood) and with anti-B serum (serum that contains antibodies against type B blood). Whether the blood cells stick together (agglutinate) in the presence of either of these serums determines the blood type. Second, in reverse typing, the patient’s serum is mixed with blood that is known to be either type A or B to watch for agglutination. A person’s blood type is confirmed by the agreement of these two tests.

Similarly, with Rh typing a sample of a person’s red blood cells is mixed with a commercially-prepared anti-serum containing anti-Rh antibodies. If agglutination occurs, then the blood is Rh-positive; if no reaction is observed, then the blood is Rh-negative. Rh testing is especially important during pregnancy because a mother and her foetus could be incompatible. If the mother is Rh-negative but the father is Rh-positive, the foetus may be positive for the Rh antigens. As a result, the mother’s body could develop antibodies against Rh, which can destroy the baby’s red blood cells. To prevent development of Rh antibodies, an Rh-negative mother with an Rh-positive partner is treated with an injection of Rh immunoglobulin during the pregnancy and again after delivery if the baby is Rh-positive.

Compatibility Testing
Compatibility testing is performed to determine if a particular unit of blood can be transfused safely into a certain patient. This includes ABO-Rh blood typing (see above), antibody screening (for unexpected red blood cell antibodies that could cause problem in the recipient), and cross-matching.

There are many antigens besides A, B, and Rh. However, neither the donor nor the recipient is tested routinely for these other antigens. But, if a patient has had a previous transfusion or been through a pregnancy, they may have developed antibodies to one of these other antigens. Therefore, it will be important in all future transfusions that the donor’s red blood cells do not have that particular antigen; otherwise, the recipient may have a transfusion reaction. The presence of such an antibody is determined by doing an antibody screening test by mixing the patient’s serum with red cells with a known antigenic makeup.

Cross-matching is performed to determine if the patient has antibodies that react with the donor’s cells. If there is a reaction, the laboratory staff will investigate further to identify the specific antibody and locate donor units that lack the antigen that matches the patient’s antibody. This unit will then be tested to confirm that this is a safe match.

It is ideal to receive a blood transfusion with blood that matches your blood type exactly. However, anyone can receive type O red blood cells in an emergency. Therefore, people with type O blood (particularly O Rh-negative) are called “universal donors.” People with type AB Rh-positive blood can be transfused with red blood cells from individuals of any ABO type and are commonly referred to as “universal recipients.

Risks

Are there risks associated with donating or receiving blood? The blood banking community assures the UK public that it is safe to donate blood. A new, sterile needle is used for each donation procedure. Therefore, you cannot get infected with viruses, such as HIV or hepatitis, by donating blood.

In addition, donors are screened before giving blood to ensure that they are in good health and have no complications that could cause them harm by donating. Mild side-effects from the procedure that a donor might experience include stinging during insertion of the needle, upset stomach, dizziness, and possibly a small amount of bruising later at the site of the blood draw. In very rare cases, a donor may faint, have muscle spasms, or suffer nerve damage.

There are some risks with receiving blood transfusions. Some people fear that they may contract an infectious disease. However, donated blood is carefully screened for transmittable diseases, as noted earlier in this article. The risk of infection from transfusion is now extremely low (about 1 in 600,000 units transfused for hepatitis B and about 1 in 2 million units transfused for HIV and hepatitis C). Of greater concern is ABO incompatibility and transfusion reactions.

ABO incompatibility occurs when blood samples from two people with different ABO blood types are mixed. The recipient of the blood transfusion could have an immune reaction against the foreign blood cells that can be very dangerous, even life-threatening. Besides just ABO incompatibility, there are other incompatibilities that can cause transfusion reactions. Antigens occur on other blood components, including white blood cells, platelets, and plasma proteins. The immune system will attack and destroy the donated blood cells, with serious side-effects for the patient.

There are several types of transfusions reactions, such as allergic and febrile (characterised by fever). Treatment will depend on the type of reaction and the patient’s symptoms (for example, antihistamines may be used to reduce rash and itching from allergic reactions while acetaminophen may be prescribed to reduce fever). Many transfusion reactions go undetected and, therefore, unreported. However, the reported rate of transfusion reactions is on the order of 1 per 1,000 components or 1 in 400 people. Nearly all of these are non-infectious complications and include mis-transfusion, volume overload, and febrile or allergic reactions.

Links

National Blood Service
British Blood Transfusion Society
Health Protection Agency – West Nile Virus
Serious Hazards of Transfusion (SHOT)
Scottish National Blood Transfusion Service