Blood groups Flashcards
How are the blood group antigens determined?
They are autosomal and co-dominant - express both products
What are the differences between the protein and glycolipid determinants of blood group antigens?
Protein gene directly codes and glycolipid gene encodes enzymes that add or remove carbohydrates or lipids from the cells - ABO
What does the Duffy blood group allow?
Malaria infection.
How do naturally occurring antibodies develop?
They develop in the absence of exposure to the red cell antigen.
Most likely stimulated by cross-reacting antigens derived from bacteria.
Not present at birth but develop within 1 year.
IgM but also some IgG.
These are usual glycolipids and initiate complement. Abs are intravascular
ABO
How do immune stimulated red cell antibodies develop?
In response to red cell antigen exposure - IgG
Usually glycoproteins, not complement or only early, extravascular
RhD
What would administering the wrong blood groups cause?
Intravascular haemolysis,
Renal failure
Disseminated intravascular coagulation
What happens when you transfer RhD +ve blood cells into an RhD -ve person?
They form anti-D antibodies, which are IgG.
Extravascular destruction of RBCs
Causes haemolytic disease of the new borne
What are some of the mminor blood group antigens?
Kell
Kidd
Duffy
Why don’t IgG antibodies cause direct agglutination of RBCs?
Because the negatively charged RBCs (zeta potential) repells other RBCs and the IgG molecules are too small to over come the zeta potential. IgM is big enough.
For the IgG agglutination, use a secondary anti-human antibody to cross-link the antibodies to cause agglutination.
What is haemolytic disease of the newborn?
Maternal IgG antibodies cross the placenta and kill foetal RBCs. Most frequently is anti-D.
Causes anaemia by killing RBCs. Pre-birth, the placenta is effective at removing dead RBCs. But if the baby is born alive then the antibodies continue to kill RBCs but the baby cant clear the dead RBCs. -> jaundice. Bilirubin can cross the blood brain barrier in infants causing inflammation and kernicterus resulting in multiple neuroabnormalities.
Why does haemolytic disease of the newborn rarely impact the first child?
Because the antibody production is insufficient to cause damage.
Memory response with second child is lethal.
How do you treat haemolytic disease of the newborn?
Give anti-D to prevent primary immunisation by coating the fetal cells in the circulation.
Give following birth and during pregnancy if chance of sensitising event, e.g. abortion, amniosentesis.
Is ABO haemolytic disease a risk?
Only very slight. IgM antibodies won’t cross placenta. ABO is also weakly expressed in infants. ABO is widely expressed in placenta and will mob up AB,
What are some tests performed on donated blood?
ABO RhD HBSAg and PCR HEp C Ab and PCR HIV Ab and PCR Serology for syphilis
What happens to a blood donation?
White blood cells are removed - cause adverse effects and no benefit.
Compatibility testing.
Centrifuge to remove the plasma rich in platelets (platelet concentrate).
Centrifuge further to remove platelets from the serum (fresh frozen plasma). Some serum goes with the RBC to reducy how sticky they are (resuspended RBCs).
What is the shelf life of RBCs, platelets and FFP?
RBCs - 35 days
Platelets = 7 days
FFP - 2 years at -25 degrees
Checklist to give RBCs?
What improvement am I tryinjg to achieve?
Can I minimise blood loss to reduce need for transfusion?
Any other treatments?
What is the specific indication for the need to transfuse for this patient?
Do the benefits of transfusion outweigh the risks?
What are the indications to give a transfusion?
Haemoglobin
Signs and symptoms of hypoxia
Ongoing blood loss
Risk of anaemia
Talylord depending if the patient has lost blood (inacurate Hb levels), has a low pulmonary function, atherosclerotic disease.
What Hb levels are an indicate for transfusion?
<70 g/l - should give
70 - 100 g/l - likely to be apropriate during surgery or with signs and symptoms
> 100 g/l not likely to be apropriate
What are the indications for transfusion of platelets?
Bone marrow failure - <10^9/L when no risk factors and <20^9 when risk factors present
Surgery - <50^9 for normal surgery and <100^9 for high risk surgery
Platelet function disorder
Bleeding
Massive haemorrhage
What do you need to consider when transfusing FFP?
The antibodies in the serum and the antigens on the recipient RBCs.
What steps do you take to ensure safe transfusion?
Correct patient identification and labeling at the bedside
Determine ABO and RhD
An antibody screen
Select appropriate RBCs for transfusion
Cross match with patient or compatibility test
Final identity check at the bedside
What are the main causes of harm with transfusion?
Transfusion related acute lung injury
Infection
Incorrect blood transfusion (human error)
What is the method to identify antibodies in serum?
Anti-human globulin technique
How is compatibility tested?
Full crossmatch - involves testing for antibodies in the recipient serum, such as anti-kell.
Immediate spin cross match
Computer cross-matching
What are the emergency RBCs?
O RhD -ve
What do you do when transferring blood?
Monitor the patient
If symptoms develop stop the transfusion
Maintain the line with saline
seek advice
What testing needs to occur prior to transfusion?
Recipient:
- Determine the ABO and RhD type of the recipient
- Do an antibody screen (anti-human Ig test)
Donor:
- blood group and screen
- Compatibility testing - full cross-match if there the Ab screen is positive in the patient (i.e. they express Kell antigen).
- Immediate spin and computer cross-match
What are the complications of transfusion?
Immunological - Early or late
Non-immunological - bacterial or viral
Early -
- haemolytic reactions
- Febrile non
- Transfusion related acute lung injury
- Reactions to proteins
Late
- delayed haemolytic reactions
- Post transfusion
- Graft vs host disease
What are the symptoms of an immediate haemolytic reaction?
Fever
Restlessness
Retrosternal or loin pain
High temp
Hypotension
Uncontrolled bleeding
What is the difference between immediate haemolytic reaction and extravascular haemolytic reaction?
The immediate (intravascular) is caused by IgM antibodies targeting ABO and inducing complement activation -> haemolysis -> DIC and hypotension
Extravascular - IgG against Rh antibodies or kell, kidd or duffy.
Don’t activate complement beyond C3. -> opsonisation
What is a delayed haemolytic reaction?
occurs 7-10 days after transfusion
Patient Hb falls and jaundice.
Is a memory response - reactivation
What is a febrile non-haemolytic transfusion reaction?
Fever
Occur because of antibodies against white blood cell antigens in the patients serum.
Hard to differentiate from acute haemolytic reaction.
