Pretransfusion Testing & Antigen Typing Flashcards
How many unique identifiers must be on the recipient’s serum/plasma sample accompanying request for pre-transfusion testing?
2 unique identifiers
How long after transfusion must the recipient’s sample and RBC segment be retained?
retained for 7 days after transfusion
If the patient was transfused with allogenic RBCs or pregnant within the last 3 months OR has unknown transfusion history, what must happen?
A serum/plasma sample must be drawn within 3 days of transfusion. (Day of draw is day 0)
A patient needs a blood transfusion today (Thursday). Their sample was collected 3 days ago on Monday. Could this sample be used for pre-transfusion testing?
Yes. Date of collection (Monday) would be day 0. Sample had to be drawn within 72 hours of transfusion, which would still be good up until Thursday.
A patient needs a blood transfusion today (Thursday). Their sample was collected 3 days ago on Monday. Could this sample be used for pre-transfusion testing?
Yes. Date of collection (Monday) would be day 0. Sample had to be drawn within 72 hours of transfusion, which would still be good up until Thursday.
What kind of tests are performed before transfusion?
ABO + Rh Type
Antibody screens
Crossmatch
Weak D testing confirmation NOT required for patients
Autocontrol not required
What is a crossmatch?
A test done in pre-transfusion testing
Helps demonstrate ABO compatibility -
Patient’s SERUM mixed with DONOR RBCs; observe for agglutination or hemolysis
What is an electronic crossmatch and when is it done?
The issue of blood without direct serological cross matching.
Done if recipient or patient has current negative antibody screen AND no prior antibody history.
- second ABO check required
What is an immediate spin crossmatch and when is it done?
to demonstrate or confirm ABO compatibility.
Patient serum mixed with donor RBCs. Does not carry thru to 37C incubation with AHG.
** Immediate spin AND electronic crossmatch done if pt current antibody screen is negative and has no prior history of clinically significant antibodies**
When does antigen typing have to be performed in pre-transfusion testing?
When a patient/recipient has significant antibodies, they must receive antigen-negative units that are crossmatch compatible.
Once you find the antigen negative units, confirm it is really compatible by antigen typing (antigen neg units type with commercial preparations of the antibody)
Calculation to find probability of finding antigen negative units
Multiple antigen-negative units compatible % together, then convert to decimal
Ex. Need to find C and Jka negative unit
C = 70% pos, 30% neg Jka = 75% pos, 25% neg
.30 x .25 = 0.075 or 7.5% –> probably need to screen ~8 units in 100 (8/100) to find one that is C & Jka negative
If you need to find 3 units that are C and Jka negative, then do 8/10=3/X, then solve for X. (38 units)
For antigen typing controls, what would be a positive control?
Test anti-sera with a heterozygous cell because it should be POSITIVE even at this lower dosage.
Ex. Anti-Kell tested with a cell that is heterozygous for big K –> Kk cell (rather than using KK)
For antigen typing, what would the negative control be?
Use a screening cell without antigen.
Example: Test Anti-K sera against a kk cell
Can Rh+ units be given in an emergency if not Rh- units are available?
Yes. RhIg should follow especially if the recipient is a women of child bearing age.
