W2 Flashcards
DAT vs IAT
DAT:
In vivo: Ab bound RBC now?
Pt’s RBC –> wash –> AHG
Use for transfusion rxn or hemolysis
IAT:
In vitro: Ab could bind RBC?
Pt’s plasma + cells + potentiator –> incubate –> wash –> AHG
Use for AbSC, crossmatching, AbID, Ag typing
* Used for both cell OR Ab
Cells for AbSC test
- Can be 2 or 3 cells.
- The 1st 2 cells always have D+, the 3rd cell will have D=
- The first cell is always homozygous C and e. The 2nd cell is flip off (c and E)
- At least 1 cell shows K
- At least 1 homozygous for Duffy a, b/ Jka, Jkb
Exclusion criteria
Zygosity: C, c, E, e, (K), k, Kpb, Jsb, S, s, M, N, Duffy, Jka, Jkb
No zygosity: D, f, Lea, Leb, P, Xga
Low frequency: Cw, Jsa, Kpa, Lua, Dia, V
Rule of 3
- Applied for suspected Ab after exclusion
- 3 positive cells for that Ag react
- 3 negative cells for that Ag not react
- 95% percentile confidence
- Followed by Confirmation testing aka Ag typing
Autocontrol
- Required for each methodology: Pt’s plasma + Pt’s RBC
- Neg: Alloantibody
- Pos: Autoantibody, Alloantibody (after transfusion - past 90 days) - DAT should be pos
Elution
- A/C is positive –> confirm with DAT
- DAT shows positive –> IgG bound on RBC
- Eluate by acid to get IgG off RBC –> IgG goes to plasma for testing.
- RBC destroyed
Transfusing antibody patient
- If significant: must get antigen negative
- If insignificant: must get compatible
- History of Abs need to be considered (different from ABO)
Unexpected Antibody
- Significant Abs:
Rh, Kell, Duffy, Kidd, MNSs, P - Insignificant Abs:
Lewis, Chido, Rogers
IgG vs IgM
IgG: Opsins, fix complement, cross the placenta, like 37C, 2 stages of sensitization and lattice formation
IgM: Opsin-ish (via complement), bind complement, not cross the placenta, some like 37C- some like colder, 2 stages happen at the same time. Destroyed by DTT. Include: LEMN P
Both can shorten RBC survival
Antigen Typing
- Determine what Ag are on pt’s or donor’s RBC
- Antisera from vendors are specially calibrated (reagent is fragile)
When will we do Ag typing
- Problem-solving: Ab ID, ABO discrepancies
- Confirm test on pt:
e. g. knew pt has Ab, confirm pt does not have Ag - Donor testing: ensure donor’s RBC is Ag negative to pt’s Ab
Antigen typing
- Patient: should be Ag negative for the present Ab, perform before transfusion if pt got multiple transfusion
(sickle cells, thalassemia) - Donor: As needed, history is a guidepost, the donation center will Ag typing/genetic testing on good donors. rare donors are stockpiled
Process of Ag typing
Depend on what type of Ab, methods can be variable
- IS
- Incubation: 37C in 15 min
- AHG
- Weird spin time
- Follow product insert
Problems with Ag typing (Cannot test if)
- Transfusion within 90 days: multiple populations
- Old specimen: follow product insert
- Positive DAT: cause false positive if using AHG (bind to IgG on RBC instead of IgG from reagent)
- Expensive, time consuming
Crossmatching
- After Ag typing and make sure the unit is Ag neg
- Use patient’s plasma, look for Ab
- Always do except when pt die
- ABO Xmatch: IS, every unit leaving the lab, test for IgM (cause acute hemolytic rxn)
- AHG Xmatch: SOPs vary, test for IgG (cause delayed hemolytic rxn), combine with Ag typing
