Week 2: ABO Discrepancies

causes of ABO discrepancies

1. ABO subgroups

2. antibody titer diminished

3. technical error

4. protein abnormalities

5. bone marrow transplants

6. cold reacting antibodies

7. bacterial enzymes

1st step to resolve an ABO discrepancy

1. repeat the test on the same sample

2. technical errors may be resolved

examples of technical errors in ABO typing

1. adding wrong reagent

2. missing plasma

3. switching tubes

4. contaminated reagents

5. recording wrong result

6. heavy cell suspension

2nd step in resolving ABO discrepancies

test a 2nd sample if the current specimen doesn’t match the historical type

what errors do testing a second sample correct?

1. error in labeling tubes

2. drawing patinet

3. documentation

what type of reactions should be investigated in ABO discrepancies?

weak reactions

what discrepancy can these factors cause?

1. bone marrow or stem cell transplants

2. antisera with contaminating antibodies

3. rouleaux

4. cold reacting antibodies

5. acquired B phenotype

6. chimerism

extra reaction in forward type

acquired B phenotype

bacterial enzyme changes the A antigen sugar to resemble B

what should be checked if a patient is suspected to have the acquired B phenotype?

patient diagnosis for GI conditions

chimerism

person with 2 genetically different RBC populations

chimerism can occur in _______

twins

the following reaction denotes what?

• anti-A = 0

• anti-B = MF+

• A1 cells = 4+

• B cells = 0

1. chimerism

2. O type and B type are present

high _______ concentrations can cause rouleaux

protein

conditions that cause rouleaux

1. multiple myeloma

2. waldenstrom macroglobulinemia

3. liver disease

resolutions for extra reaction in forward type

1. check patient history

2. wash RBC suspensions

3. warm RBC or wash with warm saline

4. acquired B

how does washing RBC suspensions help resolve discrepancies?

1. removes excess plasma proteins to fix rouleaux

2. removes antibodies to reagent component

3. wash cord cells before testing

wharton’s jelly

mucous-like connective tissue surrounding the blood vessels in a newborn's umbilical cord

how does warming or washing with warm saline resolve discrepancies?

eliminates cold antibodies and thus spontaneous agglutination

the bacterial enzyme that causes acquired B strips an _______ group from the A antigen, turning it into ___________

acetyl, galactosamine

how is an acquired B type confirmed with testing?

1. prove using auto control that the patient’s rbcs and serum do not react

2. test with acidified anti-B, which only react with true B antigens

what discrepancy will these factors cause?

1. massive transfusion of type O blood to non-O patient

2. chronic diseases (leukemia/lymphoma)

3. bone marrow or stem cell transplant

4. ABO subgroups

weak/missing reaction in forward type

some subgroups of A will react weaker or not at all with anti-A, but will react with __________

anti-A,B

what can occur in pancreatic, ovarian, and biliary tract cancers with ABO typing discrepancies?

there is too much soluble ABO antigen, and the antisera binds the soluble antigen rather than the RBC antigens → weak/missing forward rxn

what could this indicate?

patient received O RBC transfusion

what could this indicate?

patient received A RBC transfusion

resolutions for weak/missing forward reaction?

1. check patient history

2. incubate at RT or cold → enhance reactivity

3. test with anti-A,B → weak subgroups

4. wash patient RBCs to remove soluble ABO antigen

what type of discrepancy do these factors cause?

1. elevated globulin (MM, waldenstrom’s macroglobulinemia)

2. elevated fibrinogen

3. rouleaux

4. bone marrow or stem cell transplant

5. cold reacting antibody

6. IgM alloantibody

7. subgroups of a

extra reaction in back type

resolutions for extra reactions in back type

1. saline replacement

2. A1 lectin

3. cold autoadsorption

4. warming at 37C

saline replacement technique

1. tells apart true clumping vs rouleaux

2. centrifuge, remove plasma, add saline

3. true agglutination = remains +

A1 lectin

1. Dolichos biflorus

2. only agglutinates A1 antigen

how are A2 type patients confirmed through testing?

1. may develop anti-A1 → + reverse

2. add A1 lectin to patient RBC → - forward

3. add A2 cells to patient plasma → - back

autoadsorption

1. remove autoantibodies so that underlying (“masked”) alloantibodies may be identified

2. patient's RBCs are mixed with their own plasma at 4°C so the cold autoantibodies stick to the RBCs and leave the cleaned plasma behind

what discrepancy do these factors cause?

1. chronic diseases (leukemia/lymphoma)

2. bone marrow or stem cell transplant

3. age of patient (elderly or infant)

4. acquired or congenital agammaglobulinemia

weak/missing reaction in back type

why do cord blood and heel stick testing for babies not include performing a back type?

newborns do not start developing antibodies until 4 months old

resolutions with a weak/missing reaction in back type

1. check patient history

2. add more plasma

3. incubate at RT or cold

what should also be done when incubating at RT/cold to enhance reactivity in back type?

1. test against O cells → rule out cold alloantibodies

2. run auto control → rule out cold autoantibodies