Week 4- Red cell alloantibodies Flashcards
(39 cards)
when are red cell allo-antibodies formed
after a potential sensitising event e.g. transfusion, pregnancy, transplant
which antibodies are tested for in a transfusion hospital lab
only the most clinically significant antibodies i.e. those capable of causing transfusion
reactions and HDFN.
what does antibodies do in acute haemolytic reaction
- activate complement pathway
- macrophage recognition of the red cell bound antibody
what is the complement pathway
used to destroy any invading cells
e.g. bacteria, but red cell antibodies also initiate this pathway.
what is intravascular haemolysis
the final steps of the complement cascade causes ‘channels’ to be formed through the cell membrane & results in haemolysis
what are the clinical phases of acute haemolytic reaction
phase 1: haemolytic shock
Phase 2: Post shock, evidence of haemolysis
Phase 3: Oliguric
Phase 4: Diuretic
how does acute haemolytic reaction occur
- Lysis of red cells causes circulation of free haemoglobin and remnants of red cell
membrane. - This combined with complement cascade results in activation of coagulation cascade.
- Uncontrolled systemic coagulation results in disseminated intravascular coagulation (DIC):
- DIC leads to many small thromboses being deposited in vessels in most organs.
- As the clotting factors begin to be consumed, there is an increased risk of simultaneous
haemorrhage especially whilst undergoing surgery. - Death can be due to multi organ failure if DIC is untreated.
what is phase 1: haemolytic shock
Circulatory shock due to lack of red cells leads to:
* Hypotension (cytokine release leads to
vasodilation)
* Tachycardia (heart beats faster to maintain BP)
* Chills (vasoconstriction to maintain BP)
* Rapid and shallow breathing due to
sympathetic nervous system stimulation and acidosis
* Chest & lumbar pain (cytokine release constricts gut & lung smooth muscle)
* Release of inflammatory cytokines can cause a ‘sense of impending doom’ - a classic transfusion
reaction symptom
what is Phase 2: Post shock, evidence
of haemolysis
- Haemoglobinuria
- Drop in Hb
- Raised bilirubin
- Jaundice
- Blood film shows
agglutination, spherocytes, red
cell fragments
what is Phase 3: Oliguric
Free haemoglobin in the blood causes toxic acute tubular
necrosis. Leads to acute renal failure
what is phase 4: diuretic
- Renal tubules remain scarred
- Spontaneous diuresis
- Inc loss of sodium, potassium, fluid
- Leads to electrolyte imbalance
- Slow recovery or permanent renal damage
how often does ABO- incompatibility transfusion occur
around 1 in 180,000
how is ABO- incompatibility transfusion caused
human error:
- when taking or labelling pre-transfusion blood samples
- collecting components from the blood bank or satellite refrigerator
- failing to perform a correct identity check of blood pack and patient at the bedside
what is the chances of a patient being ABO incompatible if red cells are transfused incorrectly
around 30%
how many cases does major morbidity occur in due to ABO- incompatible transfusion
up to 30% and 5-10% of episodes contribute to the death of the patient
where are macrophages located
mainly in the spleen which monitor the circulating red cells for bound igG antibodies
what is extravascular haemolysis
when macrophages:
- remove the whole red cell from circulation
- remove the part of the membrane with the bound antibody (creating spherocytes)
when does extravascular haemolysis occur
more than 24 hours following transfusion
what is extravascular haemolysis usually a result of
previous alloimmunisation and subsequent undetectable level of antibody in pre-transfusion screen.
what is indirect antiglobulin test
- serum with specific antibody mixed with reagent red cells. washed 3x after incubation to remove unbound globulin
- anti-human globulin (AHG) added to promote angulation on centrifugation
what does + refer to on antibody screening cells
presence of antigen
what does 0 refer to on antibody screening cells
absence of antigen
when should antibody specificity be assigned
when the plasma is reactive with at least two
examples of reagent red cells expressing the antigen and non‐ reactive with at least two examples of reagent red cells lacking the antigen.
what is essential when one antibody specificity has been identified
that the presence or absence of additional clinically significant antibodies is established