BB - Day 4-5

Question 1

What could be a reason why we get a positive auto-control as it relates to IgM autoantibodies? How can we avoid getting a positive AC?

Answer 1

IgM autoantibodies cause complement to bind to cells. C3 interferes with AHG testing and gives us a positive AC

Use monospecific AHG

• contains anti-IgG
• polyspecific AHG contains anti-IgG and anti-C3

Question 2

If we suspect IgM antibody in the patient’s plasma, what test can we do to confirm?

Answer 2

At 4C, agglutination reactions should be stronger compared to room temperature

Question 3

If we suspect IgM antibody in the patient’s plasma causing agglutination after 37C or AHG, how can we resolve this issue?

Answer 3

Pre-warm screen: warm everything to 37C and do whole test at 37C. Avoid letting reagents or cells cool down

Question 4

After an antibody ID, we can type the patient’s and donor’s cells for the antigens corresponding to the antibodies identified. The cells should be ___ for these antigens

Answer 4

Negative

• have antibody in patient serum, so must be negative for the antigen
• donor cells must not have the antigen as well for transfusion to proceed

Question 5

Bandeiraea simplicifolia is a lectin that targets…

Answer 5

B cells (anti-B lectin)

Question 6

The major crossmatch test consists of mixing these two components

Answer 6

Patient’s serum

Donor RBCs

Question 7

The minor crossmatch test consists of mixing these two components

Answer 7

Donor’s plasma

Patient’s RBCs

Question 8

Explain why an antibody screen would be positive and a crossmatch negative. Can we proceed with the transfusion?

Answer 8

An unknown antibody in the patient’s plasma reacted with an antigen on the screen cells

Cannot proceed with transfusion until the antibody(s) is identified, and phenotyping shows the donor is negative for the corresponding antigen

Question 9

What test should we run if the antibody screen is negative but the crossmatch is positive?

Answer 9

DAT on donor cells

-positive DAT indicates cells are sensitized and AHG phase of the crossmatch will be positive

Question 10

What is phenotyping? What antigens does phenotyping look for?

Answer 10

Testing cell with known antibodies to determine antigens
-same as forward typing

Antigens other than A, B or D

Question 11

When phenotyping, what does the negative control cell ensure?

Answer 11

No false negative reaction and specificity of the anti-serum

Question 12

When choosing a positive control cell for phenotyping, the antigen should be hetero or homozygous for the antigen? Why?

Answer 12

Heterozygous

Ensures antibodies in serum are strong enough to react with a weak/heterozygous antigen
-gives confidence in the results

Question 13

After an antibody has been identified in the patient’s serum, when we perform phenotyping on the patient’s RBCs, the target antigen should be…

Answer 13

Absent (negative result)

-patients should not make antibodies against their own antigens

Question 14

Phenotyping uses either DAT or IAT. The difference between the two tests is that DAT are class ___ antibodies while IAT are class ___ antibodies.

Answer 14

IgM = incubate at room temperature
-mostly Rh group. Note: Rh antibodies mostly IgG in nature, but commercial anti-sera uses IgM

IgG = incubate at 37C for 15 mins, add AHG

Question 15

What is an antibody screen used to look for? What is the term for these antibodies?

Answer 15

Detect RBC antibodies other than the “expected” anti-A and anti-B

• anti-A and anti-B are naturally occurring IgM
• screen looks for “unexpected” antibodies

Alloantibodies

Question 16

Is the antibody screen a DAT or IAT test?

Answer 16

IAT - patient’s serum + screen cells

Question 17

What types of cells does the antibody screen test use? Why?

Answer 17

O cells

No A or B antigens expressed on O cells to bind to anti-A or anti-B, so will not interfere with detection of unexpected antibodies

Question 18

Antibody screen - are the antigens expressed on the red cells homozygous or heterozygous? Why?

Answer 18

Homozygous

Double dose of the antigen so if patient’s serum has alloantibodies, they are more likely to bind to the screen cells

Question 19

What do enhancement reagents promote? How?

Answer 19

Antigen-antibody binding/agglutination by reducing the zeta potential

Question 20

What do auto-controls check for? What does it consist of?

Answer 20

To see if patient’s serum may agglutinate own cells (autoantibodies)

Consists of patient’s cells and serum

Question 21

Enhancement solution is used for these tests… What is the exact enhancement solution called? What tubes is the enhancement solution added to?

Answer 21

Antibody screen and antibody panel

LISS

SI, SII, SIII, AC

Question 22

The difference between the antigens used in screen cells and antigens used in the positive control for phenotyping is…

Answer 22

Screen cells are homozygous for the antigen

Phenotyping positive control cells are heterozygous for the antigen

Question 23

3 most common enhancement reagents include…

Answer 23

LISS

PEG

Bovine albumin

Question 24

A DAT positive test indicates this tube is also positive…

Answer 24

Auto-control

Question 25

Antibody panels are done when one of these two tests are positive

Answer 25

Antibody screen (ABS)

DAT

Question 26

If the DAT is positive, we must perform an antibody panel. However, we must first perform a…

Answer 26

Elution

Question 27

Why would we want to do an antibody screen before an antibody identification panel?

Answer 27

Antibody ID panels are long, cumbersome and expensive. If our initial screening cells are negative and there is no agglutination for the cross-match, then there is no reason to do an antibody panel

Question 28

When identifying antibodies, what rules do we follow to “rule-in” an antibody?

Answer 28

Rule of 3: at least 3 cells positive and 3 cells negative for the antigen. Positive cells should show a positive test reaction at one of the readings.

Cells positive for the antigen should show a positive test reaction while being negative for other possible antigens.

Question 29

When identifying antibodies, what rules do we follow to “rule-out” an antibody?

Answer 29

Homozygous crossout - one is enough

Heterozygous crossout - 2 or more heterozygous crossouts required if antibody is clinically significant (anti-K), or 1 heterozygous crossout if antibody is clinically insignificant (anti-M, anti-N) or low incidence (anti-Kpa, anti-Jsa)

Question 30

The titer interpretation is observed in the tube that is the ___ dilution that produces a ___ grade macroscopically

Answer 30

Highest

1+

• with AHG
• titer is the reciprocal of the dilution