Chapter 5 ABO Discrepancies

Question 1

What is an ABO discrepancy?

Answer 1

When the forward grouping does not agree with the reverse grouping.

Note: Whatever you read in your tubes must be recorded even if it doesn’t make sense.

Cannot interpret result if there is an ABO discrepancy.

Question 2

What are some signs there is an ABO discrepancy?

Answer 2

1. Agglutination is weaker than expected (Forward typing should be 3+ to 4+ and reverse should be 2+ to 4+)
2. Expected reactions are missing
3. Extra reactions are noted.

Review slide 34, Table 5.8 on typical ABO technical Errors.

Question 3

What is the first thing you do if you encounter an ABO discrepancy?

Answer 3

Repeat testing to exclude technical error.

See slide 35 for things to watch out for (more technical errors).

Question 4

What is one of the most common reasons for ABO discrepancies in the lab?

Answer 4

Missing or weak antibodies from the newborn, elderly, pathologic etiology, or immuno-suppressive therapy for transplantation.

Question 5

What category of reasons could cause problems with patient red cell testing?

Answer 5

1. Extra antigens (A w/ acquired B antigen, B(A) phenotype, polyagglutination, rouleaux, hematopoietic progenitor cell transplants)
2. Missing or weak antigens (ABO subgroup, pathologic etiology, transplanation)
3. Mixed-field reactions (transfusion of group O to a group A, B, or AB person; Hematopoietic progenitor stem cell transplants; A3 phenotype).

Question 6

What are reasons that could cause extra antibodies that result in ABO discrepancies in serum/plasma testing?

Answer 6

Subgroups with anti-A1
Cold alloantibodies
Cold autoantibodies
Rouleaux
IVIG

Question 7

After retesting what are some of the other next steps to resolve an ABO descrepancy?

Answer 7

1. Test new sample from patient, rule out contaminants or interfering substances.
2. Check patient age and history (elderly/newborn, past transfusions, illnesses)
3. Focus on the result that seems “off”.

Question 8

What is Group A with acquired B?

Answer 8

This occurs in A1 individuals with disease of the lower GI.
Group A immunodominant sugar is altered by a bacterial deacetylating enzyme. Resembles group B and cross-reacts with anti-B.

Not as commonly discovered as newer reagent formulas are more specific. Used to resolved by using acidified anti-B.

Question 9

What is the B(A) phenotype?

Answer 9

B(A) caused by increased sensitivity of potent monoclonal anti-A reagent. [Looks like the person has A antigen but they do not.] Resolved by testing with anti-A from another manufacturer.

Question 10

What is polyagglutination?

Answer 10

Hidden antigen on the RBCs is exposed (by bacterial infection or genetic mutation) and reacts with most human sera.

Results in a person looking like they are AB when they are not for example.

Question 11

What are causes of nonspecific aggregation and what can you do about it?

Answer 11

1. Rouleaux - abnormal amounts of serum protein.
2. Wharton’s jelly - gelatinous tissue contaminant in cord blood. (Occurs in newborns)

You can wash cells and repeat testing.

This can make the blood look group AB when they are group O.

Question 12

What can happen when typing someone with ABO subgroups? How do you resolve?

Answer 12

ABO subgroups may demonstrate weak or no reactivity with anti-A and/or anti-B reagents.

It’s important to check the patient’s diagnosis, age and transfusion history.

Question 13

How may people with Hodgkin’s disease test for ABO? How do you resolve?

Answer 13

They may show weakened A and B antigen expression.

It’s important to check the patient’s diagnosis, age and transfusion history.

Question 14

What are mixed-field reactions?

Answer 14

Mixed field reactions contain both agglutinated and unagglutinated cells.

Question 15

What can cause mixed-field reactions?

Answer 15

1. Two distinct cell populations (group O RBCs transfused to a group A, B, or AB individual)
2. Bone marrow transplant.
3. stem cell transplant.
4. Chimerism.
5. A3 phenotype.
6. Tn-polyagglutinable RBCs (mutation in hematopoietic tissue)

Question 16

What can cause a false positive with A1 cells when reverse typing? How can you resolve?

Answer 16

Someone who is A2 with anti-A1.

Test with Dolichos biflorous (will not agglutinate A2 cells).
Test with 3 types each of reagent A1 and A2 red cells.

Question 17

How can you manage how cold alloantibodies affect antibody screen results?

Answer 17

Use an antibody screen with autocontrol.

Question 18

What are cold alloantibodies?

Answer 18

Antibodies specific for human RBCs that react at room temperature or below.

Most common Anti-M, Anti-P1 (rare Anti-N, Anti-Lea, last a is superscript).

Question 19

Can cold alloantibodies be found on the commercial cells?

Answer 19

Yes, they may be present.

Question 20

What are cold autoantibodies and what problem can they cause in phenotying tests?

Answer 20

Cold autoantibodies are specific for autologous antigens that react at room temperature or below. Most common Anti-I, Anti-H, and Anti-IH.

They can cause spontaneous agglutination in forward typing due to Ab coated cells and cause a reaction with the corresponding cell in reverse typing due to cold autoantibody reading with I antigens or H on commercial cells.

Question 21

Are cold autoantibodies clinically significant for phenotyping?

Answer 21

No, just interferes with testing.

Question 22

How can you know if cold autoantibodies are present?

Answer 22

Would have a positive autocontrol (mix patient plasma with patient cells) and a positive DAT.

Question 23

How do you remedy the problem of cold autoantibodies during phenotyping?

Answer 23

Warm tubes or saline or use DTT.
Warm patient plasma to remedy reverse.

Confirm what reference to saline is (saline replacement?). What does DTT stand for?

Question 24

What problem can blood samples with rouleaux cause in phenotying?

Answer 24

Rouleaux (caused by increased serum proteins that occurs in Multiple myeloma, Waldenstrom, etc.) can produce false-positive agglutination in testing.

Question 25

How are problems that occur due to missing or weak antibodies remedied in phenotying?

Answer 25

Missing or weak antibodies show weak or negative agglutination in the reverse phase of testing.

Resolve by incubating at RT for 15 mins or at 4C for 5 mins or increase amount of plasma used (use 4 drops instead of 2) in reverse typing.

Testing on newborn is the most common reason for this.

Question 26

What disease states would cause weak antibodies?

Answer 26

Disease states that would have this issue are : hypogammaglobulinemia or agammaglobulinemia, taking immunosuppressive drugs, Chronic lymphocytic leukemia or lymphoma.