Research Units are designed to provide clear summaries of results and impacts of research conducted at Canadian Blood Services. Written by Canadian Blood Services researchers in collaboration with the knowledge mobilization team, these summaries will help in further disseminating research findings to facilitate informed decision-making.
Blood type is determined by whether specific molecules (called antigens) are present or absent on the surface of red blood cells. There are over 300 red blood cell antigens and over 30 blood group systems, including the well-known ABO and Rh groups. Some combinations of antigens are far less common than others, making some blood types rarer than others. Blood is considered rare if the combination of antigens is only found in one person in 500, and is very rare if only found in one person in 1000.
At Canadian Blood Services, blood safety is paramount. At every step along the path from donor to recipient, measures are taken to protect recipients from receiving blood that contains infectious disease agents such as viruses or bacteria. Donors are screened for risk factors, blood donations are tested for infectious disease agents, and production processes and storage conditions that limit the risk are use.
Exposure to cells or tissues that are genetically different to your own, for example through blood transfusion, a tissue or organ transplant, or pregnancy, comes with a risk. If the immune system identifies these cells and tissues as foreign, it will mount an immune response against the transfused or transplanted cells or tissues. To avoid these serious reactions, the blood and tissue type of recipients and donors is determined before transfusion or transplantation. To ensure compatibility, cross-matching can also be done, using laboratory tests to determine if a specific donor is compatible with a specific recipient.
Platelets are tiny cell fragments that circulate at the periphery of the blood flow near the blood vessel wall. If they encounter damage, they become “activated”, changing shape and forming a clot. Platelets are essential for wound repair and to stop blood loss after injury. If a person has low platelet numbers or their platelets are not functioning well, they are at risk of bleeding.
Antibodies are critical elements of an immune response to combat pathogens such as harmful bacteria and viruses. Interestingly, certain antibodies can also stop an immune response - a phenomenon known as antibody-mediated immune suppression (AMIS). AMIS is used in transfusion medicine to prevent an unwanted immune response, for example, the immune response that leads to hemolytic disease of the fetus and newborn (HDFN). HDFN occurs when there is an incompatibility between a mother and her fetus’ blood type — for example, when the mother is Rh-negative and the fetus is Rh-positive. If, during the pregnancy, the mother is exposed to fetal red blood cells, her immune system recognizes the Rh-antigen as foreign and produces antibodies against it. These antibodies cross the placenta and bind to the Rh-antigen on the fetal red blood cells, triggering their destruction. HDFN can be life-threatening for the fetus or newborn. HDFN can be prevented through AMIS with an anti-D drug that suppresses the mother’s immune response against the fetal Rh-antigen. However, this treatment has limitations.
High-dose intravenous immunoglobulin (IVIg) is given to treat patients with immune and inflammatory diseases. It is usually an effective treatment that is well-tolerated. However, high-dose IVIg can cause an adverse reaction in which the patient’s red blood cells burst (hemolysis). The hemolysis is often mild and self-limiting, but it can become severe. Some patients who develop hemolysis may require transfusion of red blood cells to treat the resulting anemia.
Deferral policies for blood and plasma donors are a key element in ensuring the safety of the blood system. In the 1980s, when it was established that patients contracted HIV from blood transfusions, blood operators began to defer populations at high-risk of exposure to HIV from donating blood. In Canada and elsewhere, men who have sex with men (MSM) were specifically deferred from donating when, early on during the HIV epidemic, this population was identified as high risk.
Platelet products are currently stored at room temperature with gentle agitation. However, if the platelet unit is contaminated with bacteria, this environment allows the bacteria to grow to potentially dangerous levels. Transfusing a contaminated platelet unit can cause sepsis, a potentially fatal transfusion reaction. To mitigate the risk of contamination, the donor’s skin is disinfected with an antiseptic arm scrub and the first few millilitres of the blood collection are separated into a diversion pouch. Blood operators further reduce the risk to patients by using a short shelf life for platelet products and screening each unit for bacterial contamination.
Immune thrombocytopenia (ITP) is a blood disorder characterized by bleeding due to a shortage of platelets. The symptoms of ITP are highly variable, ranging from tiny bruises to life-threatening brain hemorrhages. Identifying ITP is difficult because there are no specific diagnostic criteria or biomarkers, apart from a low platelet count with no apparent other causes.
Maintaining a sufficient inventory of blood products for patients in need is of critical importance. The supply of Type O red blood cells is especially important because these “universal donor” products can be safely transfused to patients of any ABO blood type. This makes Type O red blood cells critical for emergency transfusions when the recipient’s blood type is unknown, or if there is an insufficient supply of ABO-matched blood products available for a patient in need.