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Year 1 POM > Blood Transfusion > Flashcards

Blood Transfusion Flashcards

1
Q

Why is the ABO system important?

A
  • Is important because people have naturally occurring antibodiesagainst any antigen NOT present on own red cells, from birth.
  • The antibodies are IgM class, reactive at 37ºC and capable of fully activating complement, so are able to cause potentially fatal haemolysis (destruction of red cells) if incompatible blood is transfused
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2
Q

How are A and B antigens formed? What is Group O?

A
  • A and B antigens on red cells are formed by adding one or other sugar residue onto a common glycoprotein and fucose stem (H antigen) on the red cell membrane.
  • Group O has neither A or B sugars – H stem only
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3
Q

How are antigens determined by corresponding genes?

A
  1. The A gene codes for an enzyme that adds N-acetyl galactosamine to the common H antigen
  2. The B gene codes for enzyme which adds galactose
    A and B genes are co-dominant
    O gene isrecessive
    e.g. If a person is blood group A - genes could be AA or OA; group B – BB or OB.
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4
Q

What is different about group O?

A

Group O blood has no ABO antigens, so is safe to give to anyone in an emergency, until the patient’s own group is known.

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5
Q

What is the Rh system?

A

-The most important antigen is D.
-Blood groups: RhD positive (if have D antigen) or RhD negative (if not).
-Genes for RhD group :
1. D gene codes for D antigen on red cell membrane.
2. d gene codes for no antigen and is recessive(no actual antigen).
Therefore:
- Group RhD negative = dd
- Group RhD positive = DD or Dd

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6
Q

What happens for people who lack the RhD antigen?

A

-People who lack the RhD antigen (ie: RhD negative) CAN make anti-D antibodies AFTER they are exposed to the RhD antigen - either by transfusion of RhD positive blood, or in women if they are pregnant with an RhD positive foetus

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7
Q

What are anti-D antibodies?

A

IgG class antibodies

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8
Q

What are the implications of anti-D antibodies?

A
  1. Future transfusion

2. HDN: haemolytic disease of the newborn

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9
Q

How are future transfusions affected?

A
  1. The patient must in future, have RhD negative blood (otherwise their anti-D would react with RhD positive blood - causesdelayed haemolytic transfusion reaction– with anaemia; high bilirubin (from breakdown of red cells); jaundice etc.).
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10
Q

How is HDN affected?

A
  1. HDN =haemolytic disease of the newborn-if RhD neg mother has anti-D, then in the next pregnancy, if fetus is RhD positive: mother’s IgG anti-D antibodies can cross the placenta (only IgG class antibodies can do this) – attach to the RhD positive red cells of the foetus and cause haemolysis of foetal red cells - if severe: hydrops fetalis and death
  2. If less severe, the baby survives but after birth, the high bilirubin levels can cause brain damage or death.
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11
Q

What is the aim with RhD?

A
  • Aim: avoid sensitisation of RhD negative patients -
  • Transfuse blood of same RhD group (no harm to give RhD negative to a positive patient - just wasteful!
  • Group O negative blood (i.e. Rh D negative) is used as emergency blood when a patient’s blood group not known (NB only 6-7% of donors are O negative).
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12
Q

What are examples of other red cell antigens?

A
  • Dozens of other antigens are present on red cells.
  • We don’t routinely match blood for all these, e.g. Rh group -C, c, E, e; others - Kell, Duffy, Kidd, etc.
  • About 8% of patients transfused will form an antibody to one or more of these antigens.
  • Once patientshave formed an antibody, we must use corresponding antigen negative blood; or else there is a risk of a delayed haemolytic reaction.
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13
Q

In order to provide ABO and Rh compatible blood for a patient needing blood transfusion, what do you need to test?

A
  • ABO & RhD blood groups on patient’s red cells.

- Anantibody screen on the patient’s plasma (known as ‘group & screen’).

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14
Q

How is an antibody screen carried out?

A
  • An antibody screen is performed to excludeany clinically significant immune antibodies:
  • Patient plasma is incubated with 2 or 3 different fully typed’screening’ red cells, which are known to possess all the blood group antigens which matter clinically.
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15
Q

What happens if the antibody screen is negative?

A

any donor blood which is ABO & RhD compatible can be given

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16
Q

What happens if the antibody screen is positive>

A
  • the antibody must be identified with the use of a large panel of red cells
  • Donor units of blood that lack the corresponding blood group antigen are then chosen for cross matching with the recipient’s plasma prior to transfusion
17
Q

What is a summary of compatibility testing before transfusing patients?

A
  1. Patient blood sample (plasma + cells).
    ABO group (test patient’s red cells with known anti-A and anti-B reagents).
    RhD group (test patient’s red cells with known anti-D and reagent).
    Select donor blood of the same ABO & RhD group.
    Antibody screen +/- antibody panel, to identify antibody/ies.
    2 . Cross-match: patient’s serum mixed with chosen donor red cells - should not react: if reacts (agglutinates) = incompatible.
18
Q

What tests are undertaken on blood donations?

A
  1. Group and screening

2. Infection testing

19
Q

What is group and screening?

A
  1. Every blood donation has the ABO and RhD blood group determined
  2. The other Rh blood groups, namely, C, c, E, e and the K blood group are determined on most donations in the UK
  3. For some, testing for further blood groups is done (eg: Fya, Fyb, Jka, Jkb etc)
  4. Every donation is tested to ensure that no strong clinically significant red cell antibodies are present in the donor’s plasma, so that any transfusions containing plasma will only contain ABO antibodies
20
Q

Describe infection testing

A
  • NB:The most important step in maintaining a safe blood supply is rigorous donor selection, using voluntary, unpaid donors and self-exclusion of individuals at high risk of transmitting blood-borne agents
  • Testing donations for the relevant agents adds to safety, but no test can pick up all infections, especially early ones, so we cannot rely on testing alone
  • The tests done on every blood donation are shown in table below. In addition, giving blood only to patients who really need it reduces the risk to patients
21
Q

What is prion disease?

A
  • Prion proteins have been found in membranes of lymphocytes and platelets and the prions of variant Creutzfeldt-Jacob disease (CJD) are found in lymphoreticular tissues
  • There have been 4 cases in the UK of variant CJD transmitted by transfusion of blood or blood products in humans, where donors who were entirely well, donated then years later developed vCJD
  • The last was around 10 years ago. A blood test to exclude any donor with vCJD is not yet available. In context, approximately 2 million blood components are transfused in England alone, each year
22
Q

How is blood collected?

A

450ml blood is collected from a donor into a sterile plastic bag containing anti-coagulant

23
Q

Why is it not efficient to use whole blood?

A
  • It is not efficient to use “whole blood” containing red cells, plasma & platelets – to transfuse patients, as most patients need only one of those components of blood
  • With improved diagnosis of coagulation factor deficiencies, aggressive chemotherapy regimens, bone marrow transplantation, and improved technology, it has become routine to treat patients only with those components which are required - for example platelets, red cells, factor VIII, etc.
24
Q

Why is component therapy useful?

A
  • Component therapy enables more efficient use of blood donations, and less waste of valuable resources
  • Also, when giving a patient a red cell transfusion for anaemia, they don’t need the excess fluid contained in the plasma part of whole blood: this just puts them at risk of fluid overload, if several units of red cells need to be transfused.Split one unit of blood by centrifuging whole bag (red cells bottom, platelets middle, plasma top) then squeeze each layer into satellite bags and cut free (closed system)
25
Q

What is 1 unit?

A

whole blood or blood products derived from one single blood donation

26
Q

Describe red cells

A
  1. 1 unit from 1 donor -‘packed cells in SAGM nutrients’ (fluid plasma removed).
  2. Shelf life 5 weeks.
  3. Stored at 4 degrees Celsius (fridge).
  4. Given through a‘blood giving set’- has filter to remove clumps/debris.
  5. Rarely need frozen red cells (National Frozen Bank) - for rare groups/ antibodies - poor recovery on thawing.
27
Q

Describe Fresh frozen plasma (FFP)

A
  1. One unit from 1 donor (300ml) can get small packs for children.
  2. Stored at -30 degrees Celsius (frozen within 6h of donation to preserve coagulation factors).
  3. Shelf life 3 years.
  4. Must thaw approx 20-30 mins before use (if too hot, proteins denature).
  5. Give ASAP – ideally within 1h or else coagulation factors degenerate at room temperature.
  6. Dose 12-15ml/kg = usually 3 units.
  7. Need to know blood group - no cross-match, just choose same group (as contains ABO antibodies, which could cause a little bit of haemolysis).
28
Q

What are the indications of FFP?

A
  1. If bleeding + abnormal coagulation test results (PT, APTT).
    - Monitor response - clinicallyand by coagulation tests.
    2.Reversal of warfarin (anticoagulant) e.g. for urgent surgery (if prothrombin complex concentrates not available).
    3.Other conditions occasionally.
    NB:Not just to replace volume/ fluid loss.
29
Q

Describe cryoprecipitate

A
  1. From frozen plasma thawed at 4-8 degrees Celsius overnight residue remains.
  2. Contains fibrinogen and factor VIII.
  3. Storage is same as FFP - store at -30 degrees Celsius for 3 years.
  4. Standard dose = from 10 donors (5 in a pack)
30
Q

What are the indications of cryoprecipitate?

A

1 . If massive bleeding and fibrinogen very low.

2 . Rarely inherited hypofibrinogenaemia.

31
Q

What are the two forms of platelet concentrate?

A
  1. Pooled platelets: platelets from 4 donations pooled constitute a single adult dose (commonest)
  2. Or from a single donor on a cell separator machine, equivalent to 4 single donations of platelets
32
Q

Describe platelet concentrate

A
  1. Store at 22 degrees Celsius (Room temp).
  2. Constantly agitated.
  3. Shelf life 7 days only - (risk of bacterial infection).
  4. Need to know blood group:no cross-match, just choose same group (as platelets have low levels of ABO antigens on, so wrong group platelets would be destroyed quickly) - and can cause RhD sensitisation, as some red cell contamination.
33
Q

What are the indications of platelet concentrate?

A

1 . Mostly haematology patients with bone marrow failure eg: leukaemia (if platelets <10 x 10 9/L).
2 . Massive bleeding or disseminated intravascular coagulation.
3 . If very low platelets and patient needs surgery.
4 . If for cardiac bypass and patient on anti-platelet drugs.
5 . One pool is usually enough - rarely need more. (Generally, platelets and FFP overused in past - limited resource and cost).

34
Q

What are blood products by fractionation of plasma?

A

Fractionated (like oil) – large pool of plasma from 1000s of blood donors:

  • Factor VIII and IX
  • Immunoglobulins
  • Albumin (2 strengths)
35
Q

Describe factor VIII and IX

A

For haemophilia A and B respectively.

  • Heat treated - viral inactivation.
  • Recombinant factor VIII or IX alternatives mostly now used instead.
36
Q

Describe immunoglobulins

A
  • Intramuscular - Specific –fractionated from plasma from selected donors who have a high titre of a specific antibody (from hyperimmune donors) e.g. anti-D, hepatitis B, varicella zoster, rabies, tetanus, CMV.
  • Intramuscular: Normal globulin - broad mix in population (eg: to protect against hepatitis A)
  • Intravenous Immunoglobulin (ivIg) – can be used in some autoimmune disorders e.g. immune thrombocytopenia
37
Q

Describe albumin (2 strengths)

A
  • 4.5% -Useful in burns, plasma exchanges, etc. Probably overused (not indicated in malnutrition).
  • 20% (salt poor)- For certain severe liver and kidney conditions only.

Year 1 POM (39 decks)

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