BLOOD GROUP

• Classification of blood type based on the presence or absence of specific antigens on the surface of red cells
• About 30 different blood groups currently recognised
• An individual’s blood type is based on the different combinations of blood group antigens
• In addition to the ABO and Rhesus systems, there are the MNS system, Kell system and Lewis system

ABO BLOOD GROUP
 

• Based on the presence or absence of two antigens (agglutinogens, A or B) on the surface of red cells
• The antigens are inherited as co-dominant traits
• These antigens are associated with specific antibodies (agglutinins). Antibodies to the ABO antigens develop in childhood through exposure to the environment and the titres peak at about the age of 10 years.
•  Blood group AB individuals have both A and B antigens on their red cells and their serum does not contain any antibodies against either A or B antigen. They can receive blood from any group but can donate blood only to another group AB individual.
• Blood group A individuals have the A antigen on their red cells and their serum contains antibodies against the B antigen. They can receive blood only from individuals of groups A or O and can donate blood to individuals with group A or AB.
• Blood group B individuals have the B antigen on the surface of their red cells and their serum contains IgM antibodies against the A antigen. They can receive blood only from individuals of groups B or O and can donate blood to individuals with group B or AB.
• Blood group O individuals do not have either A or B antigens on the surface of their red cells, but their serum contains IgM anti-A and anti-B antibodies. They can receive blood only from a group O individual, but can donate blood to individuals of any ABO blood group.
• Caucasians: O = 47%; A = 41%, B = 9%, AB = 3%
• Anti-A and anti-B antibodies are IgM and cause severe intra-vascular haemolysis of incompatible red cells

Plasma compatibility

• The donor-recipient compatibility for blood plasma is the converse of that of red cells. This is because plasma contains antibodies which would agglutinate red cells. Recipients can receive plasma of the same blood group.
• Plasma from group AB blood can be transfused to individuals of any blood group
• Group O plasma can only be transfused to group O recipients
• Individuals with blood group O can receive plasma from any blood group

TRANSFUSION OF BLOOD & BLOD PRODUCTS

• Blood components such as red cells, platelets, fresh frozen plasma and cryo-precipitate are obtained from a single donation of blood
• All blood used for transfusion in the UK is screened for  hepatitis B surface antigen, hepatitis C antibody and RNA, HIV antibody, HTLV antibody, and syphilis antibody.
• Tests for antibodies to malaria, T. cruzi and for West Nile virus RNA may be used when travel may have exposed a donor to risk of these infections.
• Some donations are tested for cytomegalovirus (CMV) antibody. CMV infection can cause serious morbidity in immunocompromised patients. The risk can be minimised by the use of CMV-seronegative blood components. Leucocyte depletion also confers some protection since the virus is associated with white blood cells.
•  CMV-seronegative and leucodepleted blood components should be used for CMV-seronegative pregnant women and intrauterine transfusions
• Clotting factors, albumin and immunoglobulins are prepared using plasma from many donors
• On average, 470ml of blood is obtained into 63ml anticoagulant and stored at 4C - shelf life = 5 weeks and over 70% of red cells should be viable
• Whole blood is rarely used and packed red cells + crystalloid / colloid used

Packed red cells

• Plasma is removed and replaced by optimal additive solution containing glucose, adenine, mannitol and sodium chloride. Blood is leukocyte-depleted by filtration. Mean volume = 330ml, haematocrit = 57%

Washed red cells

• Used in patients who have had urticarial or anaphylactic reactions

Platelet concentrates
 

• Prepared from whole blood and may be stored at 22C for up to 5 days.
• Should be group-specific.

Fresh frozen plasma
 

• Plasma from one unit of blood frozen at -30C within 6h of donation. Volume ~200ml. Used to replace clotting factors in acquired bleeding disorders.
• Should be group-specific. FFP used to treat acute major haemorrhage should be of group AB and administered with O Rh -ve packed red cells.

Cryoprecipitate
 

• Fresh frozen plasma from a single donation is allowed to thaw at 4-8C and removing the supernatant. Volume ~20ml and stored at -30C.
• Contains factor VIII, vWF and fibrinogen.
• Used in the treatment of DIC
• Maintain fibrinogen concentration above 1.5 g/dl

Factor VIII & IX concentrates
 

• Freeze-dried from pools of plasma. Recombinant coagulation factors are the treatment of choice for inherited bleeding disorders

BLOOD USE IN EMERGENCIES

• Every hospital should have a Major Haemorrhage Protocol and clinicians should be familiar with their local protocol.
• If blood is required immediately, use 2 units of O Rh negative blood (emergency stock)
• If blood required in 10-15 min, use type-specific blood (same ABO and Rh type as the patient)
• If blood required in 45-60min, use cross-matched blood