day 5 - Practical Blood Transfusion Flashcards
how is blood collected / stored
Blood is collected in CPDA-1 (citrate phosphate dextrose and adenine), an anticoagulant preservative that allows storage of red cells for up to 35 days at 4-6°C. Generally, 450 ml of blood are collected in 63 ml CPDA-1. All blood in the UK is now leucodepleted shortly after donation in the unproved belief that this may reduce the transmission of new variant CJD.
1 UNIT = WHOLE BLOOD OR COMPONENTS DERIVED FROM ONE SINGLE BLOOD DONATION
when is whole blood useful
Whole Blood: Not a good term - as blood has preservative and anticoagulant added, and is deficient in labile clotting factors and functional granulocytes and platelets. It is not therefore identical to blood that is lost through haemorrhage.
Whole blood is useful in cases of acute massive blood loss - in other cases it is wasteful (massive = > 1 blood volume loss).
what are you giving when you give red cells
Red cells suspended in an optimum additive solution: SAG-M in the UK (saline adenine glucose and mannitol). Most of the plasma is replaced by SAG-M. This is the most commonly used red cell component. There are no contraindications for use except for exchange transfusions of large volume in infants.
what are washed red cells and when are they used
Washed red cells: Red cells are frozen using glycerol as cryopreservative; shelf life 10 years. Thawing must be followed by extensive washing with saline to remove the glycerol. Once thawed the shelf life is 24 hours. Freezing of cells of rare groups enables long-term storage to provide blood for patients with antibodies to high frequency antigens, and for those with multiple antibodies.
what forms are platelets available in
Platelet concentrates: Available in two forms.
Pooled platelets - platelets from several donations (4-5) pooled to constitute a single dose.
Apheresis (cell separator) platelets - from a single donor equivalent to 5 - 6 single donations of platelets.
Usually contain 2.5-4.0 x 1011 platelets per adult dose.
indications for platelet transfusions
Indications:
a) Prophylactic:
Prophylaxis due to thrombocytopenia or defective platelet function.
In prophylaxis bleeding becomes likely when platelet count is less than 10 x 109/L, but can occur at higher levels when there is fever, infection, platelet dysfunction (e.g. post
cardiac bypass).
Thrombocytopenia with decreased platelet production especially where intensive support needed e.g. chemotherapy, bone marrow transplant, aplastic anaemia.
b) Therapeutic: for treatment of bleeding due to thrombocytopenia.
Massive blood transfusion (dilutional thrombocytopenia)
Platelet dysfunction (cardiac bypass, aspirin and non-steroidal anti-inflammatory drugs) Autoimmune thrombocytopenias (AITP): platelet transfusions not indicated because there is rapid destruction of all platelets by the autoantibody. In this disease, platelets are indicated only if there is danger of serious bleeding.
Important to monitor clinical response (not just rise in platelet count). Requirements increase if platelet antibodies are present and if there is excess consumption e.g. in hypersplenism, fever, DIC.
Dose: Standard adult dose = 2.5 - 3.0 x 1011 platelets (0.6 x 1011 platelets per 10kg wt). Ideally of the same ABO and Rh group as the recipient (platelets carry some
ABO antigens).
Recovery in recipient is approximately 60-70% of the administered dose (more if splenectomised). 90% disappear by 7 days.
what are plasma products
Plasma products: clotting factors/albumin/immunoglobulins.
Tests undertaken on blood donations
Tests undertaken on blood donations
Blood grouping: every blood donation has the ABO and RhD blood group determined.
Additionally, the other Rh blood groups, namely, C, c, E, e and the K blood group are determined on most donations in the UK.
The following microbiological tests are mandatory in the UK: Hepatitis B surface antigen (HBsAg), anti-HIV1 and 2, anti-HCV , HTLVI and syphilis antibody. Selected units are tested for antibodies to CMV, malaria and T. cruzi (Chagas’ disease).
ABO system
The ABO system is important because of the universal presence of naturally occurring antibodies that are IgM, reactive at 37°C and capable of activating complement. They are, therefore, able to cause intravascular haemolysis if incompatible blood is transfused, i.e.
Blood group O subjects - possess anti-A and anti-B
Blood group A subjects - possess circulating anti-B
Blood group B subjects - possess circulating anti-A
Blood group AB subjects - possess neither anti-A nor anti-B
the Rh system
In the Rh system, the most important antigen is D, because of its high immunogenicity.
D positive = RhD positive = Rh positive
D negative = RhD negative = Rh negative
In UK 85% of population are D positive (homozygous or heterozygous) and 15% are D negative, therefore, it is relatively common for a D negative woman to become sensitised through pregnancy, as her partner is likely to be D positive (feto-maternal leakage of red cells across the placenta occurs commonly at the time of delivery, but may also occur during late pregnancy).
what happens in blood grouping
Red cells are grouped for ABO and D by taking washed red cells, incubating with antibodies of known specificity, and observing for agglutination.
- This involves separating the recipient sample into cells (rbc) and plasma (containing the antibodies.)
- The cells are then tested against known antibodies (monoclonal) – forward group
- The plasma is then tested against known ABO and Rh cells for the ABO group – reverse group
what is a cross match?
Compatibility test between donor red cells and recipient serum = cross-match
Red cells from the blood donations selected for transfusion and patient’s serum are incubated and then tested using the antiglobulin technique. The cross-match is performed only on those serum samples from patients with a high probability of needing transfusion in surgical procedures (e.g. hip replacements) and for all non-surgical patients for whom transfusion is actually prescribed as therapy (e.g. thalassaemia major; acute haemorrhage). Unimmunised patients who are admitted for surgical procedures not associated with large blood losses (e.g. cholecystectomy) do not need cross-matched blood prior to surgery and a group and screen will suffice. If, unexpectedly and exceptionally, they require blood during surgery, a rapid cross-match can be performed, or blood of the same ABO and Rh can be issued while the cross-match is being performed.
whats an anti globulin test
Antiglobulin test (Coombs’ test)
\a. Direct antiglobulin test (DAT or direct Coombs’ test) - this test will demonstrate incomplete IgG antibodies bound to red cells but not causing agglutination. Anti-human globulin reagent is added directly to well washed red cells. If any IgG is bound to rbc (e.g. autoimmune haemolytic anaemia, mild haemolytic transfusion reaction, haemolytic disease of the newborn) then the added antiglobulin reagent causes agglutination of the IgG coated cells.
b. Indirect antiglobulin test (IAT) - is used to detect IgG antibodies free in the patient’s serum. The serum is first incubated with test red cells so that any IgG red cell antibody in the serum will bind to the test cells. The red cells are thoroughly washed to remove all the patient’s serum (including all serum IgG) and then the antiglobulin reagent is added. Agglutination will result if the test red cells bear the corresponding antigen, thus indicating that incomplete immune antibodies are present in the patient’s serum.
The crossmatch is generally an IAT between patient’s serum and donors’ red cells.
Direct antiglobulin test - detects antibody bound to patient’s red cells Indirect antiglobulin test - for antibody free in the patient’s serum
what does rhesus positive mean
Rhesus positive is equivalent to D positive and rhesus negative to D negative. In the UK 85% of the population are Rh D positive and 15% are Rh D negative. A D negative woman sensitised through pregnancy by a D positive partner will make anti-D antibodies. These do not usually cause a problem for her first Rh D positive pregnancy but any subsequent Rh D positive pregnancies run the risk of developing rhesus haemolytic disease of the newborn. Without prophylaxis, a second pregnancy has a 20% chance of fetal loss and with subsequent pregnancies the risk rises to 40%.
• Two genes for RhD groups:
– D - codes for D antigen on RBC and is dominant
– d - codes for no antigen and is recessive
• Therefore dd = no D antigen = RhD negative
DD or Dd = D antigen present = RhD positive
what are Acute haemolytic transfusion reactions (HTR)
Immediate intravascular haemolysis:
This is caused mainly by incorrect identification of the recipient, and is usually due to ABO incompatibility. The antibody immediately binds to the incompatible donor’s red cells and activates the full complement cascade leading to haemolysis. Important signs in the unconscious patient are hypotension and uncontrollable bleeding. In the conscious patient, the transfusion of even a few ml of ABO incompatible blood may cause symptoms within 1-2 min. Restlessness, a feeling of oppression, substernal pain, vomiting, abdominal or flank pain and facial flushing are common. Haemoglobinuria or haemoglobinaemia occurring during the transfusion indicate acute haemolysis. Infusion of bacterially contaminated blood has similar effects and should be excluded.
The main purpose of keeping an i.v. infusion of crystalloid solution is to prevent hypotension and to maintain the urinary output to prevent renal failure.
If DIC develops, appropriate treatment should be given.
Immediate extravascular haemolysis:
HTR may also be caused by other clinically significant antibodies in the recipient’s blood, e.g. anti-RhD, -E, -c and anti-K. However, these antibodies do not activate complement at all, or if they do, it is only up to C3 and the reactions are usually much milder. Fever and jaundice are common and haemoglobinuria may sometimes develop due to severe extravascular haemolysis.
