ABO Discrepancies

What are the four broad categories used to organize ABO discrepancies?

"Forward typing, reverse typing, extra reactions, and missing reactions."

What is the general rule of thumb when resolving an ABO discrepancy?

Trust your strongest reactions.

"When manipulating the forward or reverse grouping what must be done?"

"Both tubes must be manipulated: anti-A and anti-B for forward typing, or A1 cells and B cells for reverse typing."

What are the initial steps when investigating an ABO discrepancy?

"Review patient history; repeat ABO typing using the same specimen; wash the forward cells; perform saline replacement with the reverse grouping when appropriate; review patient testing, including the antibody screen; and check elsewhere in the lab."

What is a lectin?

"A protein, chiefly of plant origin, that binds specifically to certain sugars and can cause agglutination of particular cell types."

Which plant lectin is used as anti-A1?

Dolichos biflorus.

Which plant lectin is used as anti-H?

Ulex europaeus.

What is mixed-field agglutination?

A pattern in which some red cells agglutinate while other cells do not.

Can mixed-field reactions occur in forward or reverse typing?

"They can occur in either, although the lecture lists the common causes under forward typing."

What are causes of mixed-field reactions in forward typing?

"Previous transfusion, bone marrow transplant (BMT), chimera, and an A subtype such as A3."

How may mixed-field agglutination appear in gel testing?

As two bands.

How is a mixed-field ABO discrepancy initially resolved?

Obtain and review the patient's history.

What does the notation 4+ MF indicate in an ABO typing result?

"A 4+ mixed-field reaction: strong agglutination is present, but a second population of cells remains unagglutinated."

What is weak D?

"A D antigen that is present on the red cells in reduced quantity, producing weak or undetectable immediate reactions."

Is weak D considered a forward-typing discrepancy or a reverse-typing discrepancy?

Forward typing.

What causes weak D expression?

The lecture lists C trans D and genetic mutation.

What reaction strength may suggest weak D?

An anti-D reaction weaker than 1+ (D < 1+).

How is suspected weak D investigated?

"Perform weak D testing, taking the anti-D testing through the AHG phase."

"Does a person with weak D generally make anti-D?"

"Mostly no, according to the lecture."

How does the lecture distinguish weak D from a D variant/partial D?

Weak D has the complete D antigen in reduced quantity and generally does not make anti-D; a D variant/partial D can make anti-D.

What is the key feature of weak D described in the lecture?

"The complete D antigen is present, but in a smaller quantity."

What does the lecture call the weak D antigen?

Du antigen.

Why is anti-D testing taken to the AHG phase during weak D testing?

To detect weak expression of the D antigen that may not be detected by immediate-spin testing.

Which type of anti-D is described as more sensitive in the lecture: IgG or IgM?

IgG.

"What control is required during weak D testing and what result must it have?"

A control must be run and must be negative.

What does a positive control in weak D testing indicate?

The test is not valid for interpretation; investigate the cause before reporting the result.

Which groups does the lecture specifically identify as needing weak D testing?

Babies and donors.

What is a D variant/partial D?

A D antigen variant caused by genetic mutation in which the person may type D-positive but can produce anti-D.

What reaction pattern can be seen in a patient with a D variant?

The patient may type D-positive with reactions ranging from weak to 4+ and may have anti-D.

How is a suspected D variant/partial D investigated?

Perform weak D testing.

What causes rouleaux?

Excess plasma proteins; the lecture specifically lists multiple myeloma.

Where is rouleaux most likely to interfere with ABO typing?

"Mostly in reverse typing, although it may also affect forward typing."

How may rouleaux appear during testing?

"As weak positive reactions; microscopically, red cells appear stacked like coins."

How is rouleaux distinguished from true antigen-antibody agglutination?

"Perform saline replacement on the reverse grouping; rouleaux should disperse, while true antigen-antibody reactions remain."

What additional steps does the lecture list for resolving suspected rouleaux?

"Saline replacement on the reverse, washing the forward cells, repeating the test, and reviewing patient history."

How is saline replacement performed?

"Centrifuge the reverse grouping, remove the plasma, add saline, mix, centrifuge again, and read the result."

What happens to rouleaux after saline replacement?

The rouleaux reaction should no longer be present.

What happens to true antigen-antibody reactions after saline replacement?

They should remain reactive.

Which A subtype is emphasized as the one to know?

A2.

"Approximately what proportion of the A population is A1?"

About 80%.

"Approximately what proportion of the A population consists of A subtypes?"

About 20%.

Why can an A2 individual have an ABO discrepancy?

Some A2 individuals can make anti-A1.

Is an A2 person with anti-A1 discrepancy mainly a forward or reverse discrepancy?

Reverse typing.

How does the forward grouping of an A2 person with anti-A1 usually appear?

It looks like group A.

How does the reverse grouping of an A2 person with anti-A1 appear?

"It may look like group O, but the reaction with A1 cells is weaker than the reaction with B cells."

What is the lecture's explanation for the difference between A1 and A2?

There is both a quantitative and a qualitative difference.

How do you investigate suspected A2 with anti-A1?

Test the patient's red cells with anti-A1 lectin in the forward grouping and test the reverse grouping using A2 cells.

What result with anti-A1 lectin supports an A2 phenotype?

No reaction with anti-A1 lectin.

What reverse-cell pattern supports anti-A1 in an A2 individual?

Reaction with A1 cells but no reaction with A2 cells; the B-cell reaction reflects the patient's expected anti-B.

What is a cold antibody discrepancy?

An ABO typing discrepancy caused by a cold-reactive autoantibody or alloantibody producing extra reactions.

Do cold antibodies usually affect forward or reverse typing?

"Usually reverse typing, but they can also affect forward typing."

What may cold antibodies cause in reverse typing?

Extra reactions with reverse-grouping cells.

Can cold antibodies cause extra reactions in forward typing?

Yes. The lecture notes that cold antibodies can also affect forward typing.

How are cold antibody discrepancies resolved?

"Prewarm the test, use warm washes, and use antigen-negative cells for the reverse grouping."

Why might antigen-negative reverse cells be needed for cold antibody testing?

To avoid reactions caused by the cold antibody against an antigen on the reagent reverse cells.

Where does the lecture suggest finding antigen-negative reverse cells?

"The lecture lists Le, M, N, and P1 (shown as "LeMN PI")."

What is hypogammaglobulinemia?

A condition involving reduced gamma globulins/immunoglobulins that can lead to weak or absent reverse-grouping reactions.

Does hypogammaglobulinemia primarily affect forward or reverse typing?

Reverse typing.

What are causes of hypogammaglobulinemia listed in the lecture?

Mostly age or an underlying patient condition.

What is the characteristic ABO typing pattern in hypogammaglobulinemia?

Reverse-grouping cells show weak or no reactions.

What is the goal when resolving a hypogammaglobulinemia discrepancy?

Encourage the reverse-grouping cells to react.

How can reverse reactions be strengthened?

"Extend incubation (for example, 5 minutes instead of immediate spin), add more plasma (4 drops instead of 2), and incubate in the refrigerator."

What additional cells must be included if reverse reactions are enhanced as described?

O cells and an autocontrol (A/C).

"When modifying reverse grouping conditions what consistency rule must be followed?"

Whatever is done to one reverse cell must be done to all reverse cells.

What is cis-AB?

A rare genetic situation in which one transferase produces both A and B antigens on the red cells.

Does cis-AB primarily cause a forward or reverse discrepancy?

Forward typing.

What causes cis-AB?

A genetic mutation resulting in one transferase that produces both A and B antigens on red cells.

How strong may A and B antigen expression be in cis-AB?

"The antigens are weaker than typical A1 or B expression, although the weakening may not be substantial."

What family pattern does the lecture mention as a clue to cis-AB?

"An AB father with an O mother, or vice versa, can have an AB child."

What resolution does the lecture list for cis-AB?

None is listed.

What is acquired B?

A phenomenon in which bacterial activity modifies the A antigen so that it resembles the B antigen.

What causes acquired B?

GI-tract bacteria enter the bloodstream and modify the A antigen; the lecture notes galactosamine rather than galactose.

Does acquired B primarily affect forward or reverse typing?

Forward typing.

What is the typical acquired B reaction pattern?

A group A patient has a weak positive reaction with anti-B.

What reverse-grouping pattern is listed for acquired B?

The autocontrol (A/C) is negative.

How does the lecture recommend resolving acquired B?

Use reagents from a different manufacturer.

What is B(A)?

"A phenotype in which B transferase is somewhat indiscriminate and attaches a small amount of N-acetylgalactosamine, producing weak A-like reactivity."

What causes the B(A) phenotype?

An autosomal dominant trait; the B transferase attaches a small amount of N-acetylgalactosamine.

Does B(A) primarily cause a forward or reverse discrepancy?

Forward typing.

What is the typical B(A) forward-typing pattern?

Strong reaction with anti-B and weak reaction with anti-A.

With which anti-A monoclonal antibody does the lecture say B(A) may be observed?

MHO4.

How does the lecture recommend resolving a B(A) discrepancy?

Use different antisera.

What examples of causes of weak forward reactions are listed at the end of the lecture?

"Malignancy, Ax, Ael, and transplant."

What does Ax refer to in the context of ABO discrepancies?

An A subgroup associated with weak forward reactions.

What does Ael refer to in the context of ABO discrepancies?

A very weak A subgroup associated with weak forward reactions.

Which discrepancy is associated with excess plasma proteins and coin-stack appearance?

Rouleaux.

"Which discrepancy is associated with previous transfusion

BMT, chimera, or A3?",Mixed-field agglutination.

Which discrepancy is associated with a weak anti-D reaction and testing at AHG?

Weak D.

Which D-related condition can type D-positive but may produce anti-D?

A D variant/partial D.

Which discrepancy is associated with an A2 individual making anti-A1?

A2 with anti-A1.

Which discrepancy is associated with cold autoantibodies or alloantibodies causing extra reactions?

Cold antibody interference.

Which discrepancy is associated with weak or absent reverse reactions due to low immunoglobulins?

Hypogammaglobulinemia.

Which discrepancy involves one transferase producing both A and B antigens?

Cis-AB.

Which discrepancy occurs when bacterial activity makes an A antigen resemble B?

Acquired B.

Which phenotype produces strong anti-B and weak anti-A reactions?

B(A).

What is the central difference between forward and reverse typing?

Forward typing tests patient red-cell antigens with known antisera; reverse typing tests patient plasma against known reagent red cells.

"If the forward grouping is strong but the reverse grouping is weak what general discrepancy category should be considered?"

"A missing or weak reverse reaction, such as hypogammaglobulinemia or an A subgroup with anti-A1, depending on the reaction pattern."

"If extra reactions appear in the reverse grouping what causes from the lecture should be considered?"

"Rouleaux, cold antibodies, and anti-A1 in an A2 individual."

"If extra reactions appear in the forward grouping what causes from the lecture should be considered?"

"Mixed-field reactions, weak D/D variants, rouleaux, cold antibodies, cis-AB, acquired B, B(A), and weakly expressed A subgroups."

Why is patient history important when resolving an ABO discrepancy?

"It may reveal transfusion, bone marrow transplant, underlying conditions, or other clinical information that explains the reaction pattern."