Pre-Transfusion Testing Flashcards by Timothy Carll

Blood component ABO requirements:

Whole blood, red blood cells

Whole blood should ideally be identical to recipient. It must be compatible with patient’s plasma.
Red blood cells must be compatible with patient’s plasma.

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Blood component ABO requirements:

Granulocytes, plasma

Granulocytes must be compatibel with patient’s plasma.

Plasma must be compatible with patient’s red cells (trials of group A plasma in effect)

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Blood component ABO requirements:

Platelets, cryoprecipitated antihemophilic factor

Platelets: ABO identical is better than red-cell compatible than none.
Cryo: All ABO groups are acceptable.

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What is the difference between a type and hold, type and screen, and type and cross?

Type and hold: No antibody testing.
Type and screen: Standard, includes Ab screen.
Type and cross: Includes crossmatch that allocates units to patient.

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What are some causes of false-positive results in antiglobulin testing?

Cells may be agglutinating before washing
Contaminants (dust/dirt/fibrin)
Improper procedures (overcentrifugation)
DAT+ cells
Complement (mostly C4)

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What are some causes of false-negative results in antiglobulin testing

Neutralization of AHG reagent
Interruption in testing (dissociation of IgG)
Improper reagent storage (AHG or cells)
Improper procedures (undercentrifugation)
Complement
Saline (pH, temperature)

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What can cause incompatible IS crossmatch with a negative antibody screen?

ABO incompatibility
Polyagglutination
Anti-A1 in an A2/A2B patient
Room-temperature alloantibodies (eg Anti-M)
Rouleaux
Cold autoantibodies
Passive anti-A or anti-B

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What can cause incompatible AHG crossmatch with a negative antibody screen?

DAT+
Variable antigen strength
Antibody to low-incidence antigen
Passive anti-A or anti-B

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Why may a crossmatch be compatible even if an antibody screen is positive?

Donor lacks the relevant antigen
Anti-H or Anti-LebH (with non-O donor unit)
Dependence on reagent red cell diluent
Dosage/variable antigen strength

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How many samples are affected by WBIT errors?

1:2000

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Why may a pre-transfusion specimen be rejected?

Inability to confirm identity
Hemolyzed or lipemic sample
Wrong tube type (plasma, not serum)

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What factors influence the Coombs reaction?

Temperature, Ig class, and most importantly specific Ab-Ag interactions.

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What percentage of alloantibodies fade in 1 yr? In 10 yrs?

1yr: 30%
10yrs: 50%

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How safe is it to give O-positive units to men and older women?

Safe; significant hemolysis to Rh or other antigens on group O RBCs are very rare. Some hemolysis is probably permissible in this context anyway.

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How can red cell alloantibodies be detected in the presence of a warm autoantibody?

Perform autologous adsorption to remove the autoantibody. If the patient was recently transfused, will have to use alloadsorption instead.

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What is the effect of ABO-matching (or mismatching) platelets?

ABO-identical platelets reduce refractoriness but have no effect on mortality or bleeding events.

Major mismatched platelets are less effective (knocked out), minor mismatched may cause hemolysis (carrier anti-A/B).

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What is the risk of Rh alloimmunization with platelets?

Low; platelets do not express Rh, but beware contaminating red cells. Can reduce risk by using apheresis platelets, giving to immunosuppressed patients, or using RhoGAM.

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What is the most common cause of platelet refractoriness?

Non-immune causes, including DIC< active bleeding, splenism and drug effects.

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How do platelets cause HLA immunization?

Platelets do express HLA class I antigens, but reaction is usually due to passenger leukocytes.

Rabbit erythrocyte stroma (RESt)

Commercial reagent used to remove cold agglutinins (usually Anti-Ii/HI), but can also adsorb clinically significant antibodies as well.

How can IgMs be subtracted from plasma?

Adsorption
Pre-warming
0.01M DTT

ABO discrepancies: What are some causes for weak/missing red cell reactivity?

ABO subgroups
Leukemia/malignancy
Transfusion
Pregnancy
Intrauterine fetal transfusion
Transplantation
Excessive soluble blood group substance

ABO discrepancies: What are some causes for extra red cell reactivity?

Autoagglutinins/excess coating
Unwashed red cells (plasma proteins, reagent antibody)
Transplantation
Acquired B or other polyagglutinable conditions
cisAB or B(A) phenomenon
Out-of-group transfusion

ABO discrepancies: What are some causes for mixed-field red cell reactivity?

ABO subgroup
Recent transfusion
Transplantation
Fetomaternal hemorrhage
Chimerism

ABO discrepancies: What are some causes for missing serum reactivity?

``` Age-related ABO subgroup Hypogammaglobulinemia Transplant Excessive anti-A/B (prozone) Hemodilution ```

ABO discrepancies: What are some causes for extra serum reactivity?

``` Cold agglutinins Excess serum protein Reagent antibody Transfusion of plasma products Transplantation IVIG ```

What antigens degrade over time on reagent cells?

Duffy antigens, M, P1, Kn(a), McC(a), Bg)

In what setting is plasma NOT interchangeable with serum for pre-transfusion testing?

Any testing involving complement (eg. Anti-C3 DAT). You must use SERUM in this context.

What should all reagent red cells be typed for?

D, C/c, E/e, K, Fya/b, Jka/b, MNS, P1, Le

Give 3 examples of enhancement media?

LISS, PEG, 6-22% albumin

What antigens are more strongly expressed on cord red cells?

i, LW(a), LW(b)

When would a polyspecific AHG be preferred to a monospecific AHG?

To detect complement binding/activation, such as with JK antibodies.

What medical conditions should be considered in interpreting antibody results?

Cold agglutinin disease, Reynaud, mycoplasma pnuemonia, PCH, SLE, CLL, MM, LPL/WM

What is the difference between an autocontrol and DAT?

Autocontrols reflect in vitro conditions with contributions from reagents and artificial incubation settings.

Why can't PEG tests be read directly after centrifugation?

PEG will cause nonspecific aggregation, it must be washed out after incubation.

What number of cells must be used to perform rule-ins?

Three positive reactive cells and three non-reactive negative cells.

How do cold autoantibodies present on testing? How can they be subtracted?

Gels often look mixed field; correct by warming, using RESt, or cold adsorption.

What antibodies to high-frequency antigens should be considered in white, black, and asian populations?

White: -k, -Kp(b) Black: -U, -Js(b), -Hy, -Jo(a), -Cr(a) Asian: -Di(b)

How do rouleaux cause problems in testing? How are they managed?

Can cause ABO discrepancies and DAT false positives. Treated by washing (never a problem on IAT).

What trick can you use to isolate sickle cells from donor transfused red cells?

Use hypotonic saline; sickle cells resist lysis.

When obtaining cells for phenotyping, a positive DAT will preclude accurate phenotyping. What should you do to remove IgGs/IgMs?

Wash/elute off IgGs, use 0.01M DTT to remove coated IgMs (or, pre-warm)

What antigens are enhanced by ficin/papain?

Rh, Kidd | ABO, I, P, Le

Give some examples of antibody inhibitors

Mostly just soluble antigens, useful for subtracting antibodies or confirming identity. Lewis, P1, Sda, Ch/Rg

What methods are usable for elution?

Heat/freeze-thaw only for ABO reactions. | Acid/solvent for all others.

What significant antibodies may not be reactive on IAT/37C?

- Vel - P - PP1Pk (-Tj(a)) - H