Donors are screened for health risks that might make the donation unsafe for the recipient. Some of these restrictions are controversial, such as restricting donations from men who have sex with men for HIV risk.[19] Autologous donors are not always screened for recipient safety problems since the donor is the only person who will receive the blood.[20] Donors are also asked about medications such as dutasteride since they can be dangerous to a pregnant woman receiving the blood.[21]
Donors are examined for signs and symptoms of diseases that can be transmitted in a blood transfusion, such as HIV, malaria, and viral hepatitis. Screening may extend to questions about risk factors for various diseases, such as travel to countries at risk for malaria or variant Creutzfeldt-Jakob Disease (vCJD).[22] These questions vary from country to country. For example, while Québec may defer donors who lived in the United Kingdom for risk of vCJD,[23] donors in the United Kingdom are only restricted for vCJD risk if they have had a blood transfusion in the United Kingdom.[24]
[edit] Donor safety
The donor is also examined and asked specific questions about their medical history to make sure that donating blood isn't hazardous to their health. The donor's hematocrit or hemoglobin level is tested to make sure that the loss of blood will not make them anemic, and this check is the most common reason that a donor is ineligible.[25] Pulse, blood pressure, and body temperature are also evaluated. Elderly donors are sometimes also deferred on age alone because of health concerns.[26] The safety of donating blood during pregnancy has not been studied thoroughly and pregnant women are usually deferred.[27]
[edit] Blood testing
The donor's blood type must be determined if the blood will be used for transfusions. The collecting agency usually identifies whether the blood is type A, B, AB, or O and the donor's Rh (D) type and will screen for antibodies to less common antigens. More testing, including a crossmatch, is usually done before a transfusion. Group O is often cited as the "universal donor"[28] but this only refers to red cell transfusions. For plasma transfusions the system is reversed and AB is the universal donor type.[29]
Most blood is tested for diseases, including some STDs.[30] The tests used are high-sensitivity screening tests and no actual diagnosis is made. Some of the test results are later found to be false positives using more specific testing.[31] False negatives are rare, but donors are discouraged from using blood donation for the purpose of anonymous STD screening because a false negative could mean a contaminated unit. The blood is usually discarded if these tests are positive, but there are some exceptions, such as autologous donations. The donor is generally notified of the test result.[32]
Donated blood is tested by many methods, but the core tests recommended by the World Health Organization are these four:
Hepatitis B Surface Antigen
Antibody to Hepatitis C
Antibody to HIV, usually subtypes 1 and 2
Serologic test for Syphilis
The WHO reported in 2006 that 56 out of 124 countries surveyed did not use these basic tests on all blood donations.[13]
A variety of other tests for transfusion transmitted infections are often used based on local requirements. Additional testing is expensive, and in some cases the tests are not implemented because of the cost.[33] These additional tests include other infectious diseases such as West Nile Virus.[34] Sometimes multiple tests are used for a single disease to cover the limitations of each test. For example, the HIV antibody test will not detect a recently infected donor, so some blood banks use a p24 antigen or HIV nucleic acid test in addition to the basic antibody test to detect infected donors during that period. Cytomegalovirus is a special case in donor testing in that many donors will test positive for it.[35] The virus is not a hazard to a healthy recipient, but it can harm infants[36] and other recipients with weak immune systems.[35]
[edit] Obtaining the blood
A donor's arm at various stages of donation. The two photographs on the left show a blood pressure cuff being used as a tourniquet.
There are two main methods of obtaining blood from a donor. The most frequent is simply to take the blood from a vein as whole blood. This blood is typically separated into parts, usually red blood cells and plasma, since most recipients need only a specific component for transfusions. The other method is to draw blood from the donor, separate it using a centrifuge or a filter, store the desired part, and return the rest to the donor. This process is called apheresis, and it is often done with a machine specifically designed for this purpose.
For direct transfusions a vein can be used but the blood may be taken from an artery instead.[37] In this case, the blood is not stored and is pumped directly from the donor into the recipient. This was an early method for blood transfusion and is rarely used in modern practice.[38] It was phased out during World War II because of problems with logistics, and doctors returning from treating wounded soldiers set up banks for stored blood when they returned to civilian life.[39]
[edit] Site preparation and drawing blood
The blood is drawn from a large arm vein close to the skin, usually the median cubital vein on the inside of the elbow. The skin over the blood vessel is cleaned with an antiseptic such as iodine or chlorhexidine[40] to prevent skin bacteria from contaminating the collected blood[40] and also to prevent infections where the needle pierced the donor's skin.[41]
A large[42] needle (16 to 17 gauge) is used to minimize shearing forces that may physically damage red blood cells as they flow through the needle.[43] A tourniquet is sometimes wrapped around the upper arm to increase the pressure of the blood in the arm veins and speed up the process. The donor may also be prompted to hold an object and squeeze it repeatedly to increase the blood flow through the vein.
A mechanical tray agitates the bag to mix the blood with anticoagulants and prevent clotting.
[edit] Whole blood
The most common method is collecting the blood from the donor's vein into a container. The amount of blood drawn varies from 200 milliliters to 550 milliliters depending on the country, but 450-500 milliliters is typical.[35] The blood is usually stored in a plastic bag that also contains sodium citrate, phosphate, dextrose, and sometimes adenine. This combination keeps the blood from clotting and preserves it during storage.[44] Other chemicals are sometimes added during processing.
The plasma from whole blood can be used to make plasma for transfusions or it can also be processed into other medications using a process called fractionation. This was a development of the dried plasma used to treat the wounded during World War II and variants on the process are still used to make a variety of other medications.[45] [46]
[edit] Apheresis
Main articles: Apheresis, Plasmapheresis, and Plateletpheresis
A relatively large needle is used for blood donations.
Usually the component returned is the red blood cells, the portion of the blood that takes the longest to replace. Using this method an individual can donate plasma or platelets much more frequently than they can safely donate whole blood. These can be combined, with a donor giving both plasma and platelets in the same donation.
Platelets can also be separated from whole blood, but they must be pooled from multiple donations. From three to ten units of whole blood are required for a therapeutic dose.[47] Plateletpheresis provides at least one full dose from each donation.
Plasmapheresis is frequently used to collect source plasma that is used for manufacturing into medications much like the plasma from whole blood. Plasma collected at the same time as plateletpheresis is sometimes called concurrent plasma.
Apheresis is also used to collect more red blood cells than usual in a single donation and to collect white blood cells for transfusion.[48][49]
[edit] Recovery and time between donations
Donors are usually kept at the donation site for 10–15 minutes after donating since most adverse reactions take place during or immediately after the donation. [50] Blood centers typically provide light refreshments such as tea and biscuits or a lunch allowance to help the donor recover.[51] The needle site is covered with a bandage and the donor is directed to keep the bandage on for several hours.[2]
Donated plasma is replaced after 2-3 days.[52] Red blood cells are replaced by bone marrow into the circulatory system at a slower rate, on average 36 days in healthy adult males. In that study, the range was 20 to 59 days for recovery.[53] These replacement rates are the basis of how frequently a donor can give blood.
Plasmapheresis and plateletpheresis donors can give much more frequently because they do not lose significant amounts of red cells. The exact rate of how often a donor can donate differs from country to country. For example, plasma donors in the United States are allowed to donate large volumes twice a week and could nominally give 83 liters (about 22 gallons) in a year, whereas the same donor in Japan may only donate every other week and could only donate about 16 liters (about 4 gallons) in a year.[54] Red blood cells are the limiting step for whole blood donations, and the frequency of donation varies widely. In Hong Kong it is from three to six months,[55] in Australia it is twelve weeks, [56] in the United States it is eight weeks [57] and in the UK it is usually sixteen weeks but can be as little as twelve.[58]
[edit] Complications
Donors are screened for health problems that would put them at risk for serious complications from donating. First-time donors, teenagers, and women are at a higher risk of a reaction.[59][60] One study showed that 2% of donors had an adverse reaction to donation.[61] Most of these reactions are minor. A study of 194,000 donations found only one donor with long-term complications.[62] In the United States, a blood bank is required to report any death that might possibly be linked to a blood donation. An analysis of all reports from October 2004 to September 2006 evaluated 22 events and found no deaths related to donation, though one could not be ruled out.[63]
Bruising three days after donation
Hypovolemic reactions can occur because of a rapid change in blood pressure. Fainting is generally the worst problem encountered.[64]
The process has similar risks to other forms of phlebotomy. Bruising of the arm from the needle insertion is the most common concern. One study found that less than 1% of donors had this problem.[65] A number of less common complications of blood donation are known to occur. These include arterial puncture, delayed bleeding, nerve irritation, nerve injury, tendon injury, thrombophlebitis, and allergic reactions. .[66]
Donors sometimes have adverse reactions to the sodium citrate used in apheresis collection procedures to keep the blood from clotting. Since the anticoagulant is returned to the donor along with blood components that are not being collected, it can bind the calcium in the donor's blood and cause hypocalcemia.[67] These reactions tend to cause tingling in the lips, but may cause convulsions or more serious problems. Donors are sometimes given calcium supplements during the donation to prevent these side effects.[68]
In apheresis procedures, the red blood cells are often returned. If this is done manually and the donor receives the blood from a different person, a transfusion reaction can take place. Manual apheresis is extremely rare in the developed world because of this risk and automated procedures are as safe as whole blood donations.[69]
The final risk to blood donors is from equipment that has not been properly sterilized. In most cases, the equipment that comes in direct contact with blood is discarded after use.[70] Re-used equipment was a significant problem in China in the 1990s, and up to 250,000 blood plasma donors may have been exposed to HIV from shared equipment.[71][72]
Donors are examined for signs and symptoms of diseases that can be transmitted in a blood transfusion, such as HIV, malaria, and viral hepatitis. Screening may extend to questions about risk factors for various diseases, such as travel to countries at risk for malaria or variant Creutzfeldt-Jakob Disease (vCJD).[22] These questions vary from country to country. For example, while Québec may defer donors who lived in the United Kingdom for risk of vCJD,[23] donors in the United Kingdom are only restricted for vCJD risk if they have had a blood transfusion in the United Kingdom.[24]
[edit] Donor safety
The donor is also examined and asked specific questions about their medical history to make sure that donating blood isn't hazardous to their health. The donor's hematocrit or hemoglobin level is tested to make sure that the loss of blood will not make them anemic, and this check is the most common reason that a donor is ineligible.[25] Pulse, blood pressure, and body temperature are also evaluated. Elderly donors are sometimes also deferred on age alone because of health concerns.[26] The safety of donating blood during pregnancy has not been studied thoroughly and pregnant women are usually deferred.[27]
[edit] Blood testing
The donor's blood type must be determined if the blood will be used for transfusions. The collecting agency usually identifies whether the blood is type A, B, AB, or O and the donor's Rh (D) type and will screen for antibodies to less common antigens. More testing, including a crossmatch, is usually done before a transfusion. Group O is often cited as the "universal donor"[28] but this only refers to red cell transfusions. For plasma transfusions the system is reversed and AB is the universal donor type.[29]
Most blood is tested for diseases, including some STDs.[30] The tests used are high-sensitivity screening tests and no actual diagnosis is made. Some of the test results are later found to be false positives using more specific testing.[31] False negatives are rare, but donors are discouraged from using blood donation for the purpose of anonymous STD screening because a false negative could mean a contaminated unit. The blood is usually discarded if these tests are positive, but there are some exceptions, such as autologous donations. The donor is generally notified of the test result.[32]
Donated blood is tested by many methods, but the core tests recommended by the World Health Organization are these four:
Hepatitis B Surface Antigen
Antibody to Hepatitis C
Antibody to HIV, usually subtypes 1 and 2
Serologic test for Syphilis
The WHO reported in 2006 that 56 out of 124 countries surveyed did not use these basic tests on all blood donations.[13]
A variety of other tests for transfusion transmitted infections are often used based on local requirements. Additional testing is expensive, and in some cases the tests are not implemented because of the cost.[33] These additional tests include other infectious diseases such as West Nile Virus.[34] Sometimes multiple tests are used for a single disease to cover the limitations of each test. For example, the HIV antibody test will not detect a recently infected donor, so some blood banks use a p24 antigen or HIV nucleic acid test in addition to the basic antibody test to detect infected donors during that period. Cytomegalovirus is a special case in donor testing in that many donors will test positive for it.[35] The virus is not a hazard to a healthy recipient, but it can harm infants[36] and other recipients with weak immune systems.[35]
[edit] Obtaining the blood
A donor's arm at various stages of donation. The two photographs on the left show a blood pressure cuff being used as a tourniquet.
There are two main methods of obtaining blood from a donor. The most frequent is simply to take the blood from a vein as whole blood. This blood is typically separated into parts, usually red blood cells and plasma, since most recipients need only a specific component for transfusions. The other method is to draw blood from the donor, separate it using a centrifuge or a filter, store the desired part, and return the rest to the donor. This process is called apheresis, and it is often done with a machine specifically designed for this purpose.
For direct transfusions a vein can be used but the blood may be taken from an artery instead.[37] In this case, the blood is not stored and is pumped directly from the donor into the recipient. This was an early method for blood transfusion and is rarely used in modern practice.[38] It was phased out during World War II because of problems with logistics, and doctors returning from treating wounded soldiers set up banks for stored blood when they returned to civilian life.[39]
[edit] Site preparation and drawing blood
The blood is drawn from a large arm vein close to the skin, usually the median cubital vein on the inside of the elbow. The skin over the blood vessel is cleaned with an antiseptic such as iodine or chlorhexidine[40] to prevent skin bacteria from contaminating the collected blood[40] and also to prevent infections where the needle pierced the donor's skin.[41]
A large[42] needle (16 to 17 gauge) is used to minimize shearing forces that may physically damage red blood cells as they flow through the needle.[43] A tourniquet is sometimes wrapped around the upper arm to increase the pressure of the blood in the arm veins and speed up the process. The donor may also be prompted to hold an object and squeeze it repeatedly to increase the blood flow through the vein.
A mechanical tray agitates the bag to mix the blood with anticoagulants and prevent clotting.
[edit] Whole blood
The most common method is collecting the blood from the donor's vein into a container. The amount of blood drawn varies from 200 milliliters to 550 milliliters depending on the country, but 450-500 milliliters is typical.[35] The blood is usually stored in a plastic bag that also contains sodium citrate, phosphate, dextrose, and sometimes adenine. This combination keeps the blood from clotting and preserves it during storage.[44] Other chemicals are sometimes added during processing.
The plasma from whole blood can be used to make plasma for transfusions or it can also be processed into other medications using a process called fractionation. This was a development of the dried plasma used to treat the wounded during World War II and variants on the process are still used to make a variety of other medications.[45] [46]
[edit] Apheresis
Main articles: Apheresis, Plasmapheresis, and Plateletpheresis
A relatively large needle is used for blood donations.
Usually the component returned is the red blood cells, the portion of the blood that takes the longest to replace. Using this method an individual can donate plasma or platelets much more frequently than they can safely donate whole blood. These can be combined, with a donor giving both plasma and platelets in the same donation.
Platelets can also be separated from whole blood, but they must be pooled from multiple donations. From three to ten units of whole blood are required for a therapeutic dose.[47] Plateletpheresis provides at least one full dose from each donation.
Plasmapheresis is frequently used to collect source plasma that is used for manufacturing into medications much like the plasma from whole blood. Plasma collected at the same time as plateletpheresis is sometimes called concurrent plasma.
Apheresis is also used to collect more red blood cells than usual in a single donation and to collect white blood cells for transfusion.[48][49]
[edit] Recovery and time between donations
Donors are usually kept at the donation site for 10–15 minutes after donating since most adverse reactions take place during or immediately after the donation. [50] Blood centers typically provide light refreshments such as tea and biscuits or a lunch allowance to help the donor recover.[51] The needle site is covered with a bandage and the donor is directed to keep the bandage on for several hours.[2]
Donated plasma is replaced after 2-3 days.[52] Red blood cells are replaced by bone marrow into the circulatory system at a slower rate, on average 36 days in healthy adult males. In that study, the range was 20 to 59 days for recovery.[53] These replacement rates are the basis of how frequently a donor can give blood.
Plasmapheresis and plateletpheresis donors can give much more frequently because they do not lose significant amounts of red cells. The exact rate of how often a donor can donate differs from country to country. For example, plasma donors in the United States are allowed to donate large volumes twice a week and could nominally give 83 liters (about 22 gallons) in a year, whereas the same donor in Japan may only donate every other week and could only donate about 16 liters (about 4 gallons) in a year.[54] Red blood cells are the limiting step for whole blood donations, and the frequency of donation varies widely. In Hong Kong it is from three to six months,[55] in Australia it is twelve weeks, [56] in the United States it is eight weeks [57] and in the UK it is usually sixteen weeks but can be as little as twelve.[58]
[edit] Complications
Donors are screened for health problems that would put them at risk for serious complications from donating. First-time donors, teenagers, and women are at a higher risk of a reaction.[59][60] One study showed that 2% of donors had an adverse reaction to donation.[61] Most of these reactions are minor. A study of 194,000 donations found only one donor with long-term complications.[62] In the United States, a blood bank is required to report any death that might possibly be linked to a blood donation. An analysis of all reports from October 2004 to September 2006 evaluated 22 events and found no deaths related to donation, though one could not be ruled out.[63]
Bruising three days after donation
Hypovolemic reactions can occur because of a rapid change in blood pressure. Fainting is generally the worst problem encountered.[64]
The process has similar risks to other forms of phlebotomy. Bruising of the arm from the needle insertion is the most common concern. One study found that less than 1% of donors had this problem.[65] A number of less common complications of blood donation are known to occur. These include arterial puncture, delayed bleeding, nerve irritation, nerve injury, tendon injury, thrombophlebitis, and allergic reactions. .[66]
Donors sometimes have adverse reactions to the sodium citrate used in apheresis collection procedures to keep the blood from clotting. Since the anticoagulant is returned to the donor along with blood components that are not being collected, it can bind the calcium in the donor's blood and cause hypocalcemia.[67] These reactions tend to cause tingling in the lips, but may cause convulsions or more serious problems. Donors are sometimes given calcium supplements during the donation to prevent these side effects.[68]
In apheresis procedures, the red blood cells are often returned. If this is done manually and the donor receives the blood from a different person, a transfusion reaction can take place. Manual apheresis is extremely rare in the developed world because of this risk and automated procedures are as safe as whole blood donations.[69]
The final risk to blood donors is from equipment that has not been properly sterilized. In most cases, the equipment that comes in direct contact with blood is discarded after use.[70] Re-used equipment was a significant problem in China in the 1990s, and up to 250,000 blood plasma donors may have been exposed to HIV from shared equipment.[71][72]
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