ABO Discrepancies

Question 1

List 3 technical errors that could cause a type discrepancy.

Answer 1

Failure to add reagent, failure to add sample, incorrect identification of sample, did not follow instructions, over/undercentrifugation, faulty equipment, contamination of reagents

Question 2

List 4 reasons why a patient’s antibodies in the reverse group would be weaker.

Answer 2

Newborns, elderly, leukemia, immunodeficiency diseases, immunosuppressive drugs, bone marrow transplant

Question 3

How would you resolve a type where the antibodies in the back type were not demonstrating?

Answer 3

Add two more drops of plasma, incubate the back type at room temperature for 15-30 minutes. If it still doesn’t work, incubate at 4C.

Question 4

When incubating a back type at 4C, why is necessary to also perform an autocontrol and an O cell control?

Answer 4

4C will enhance other cold agglutinins and cold autoantibodies that may be present. If the controls are positive, then you know that the extra reactivity is due to the autoantibody and not anti-A or Anti-B. if the controls are negative, then the reactivity in the A and B cell tubes during testing will be due to anti-A or anti-B present in the plasma.

Question 5

List 3 reasons that weak or missing antigens may occur in the front type.

Answer 5

Subgroups of A or B, Leukemia, Hodgkin’s Disease, Aquired B phenomenon

Question 6

In which blood group might you seen the acquired B phenomenon when testing their blood type?

Answer 6

Type A

Question 7

With which conditions are you most likely to see the acquired B phenomenon?

Answer 7

Diseases of the digestive tract

Question 8

How is an acquired B antigen formed on the red cell?

Answer 8

Blood comes in contact with bacterial enzymes that remove the acetyl group from group A blood. The resulting sugar is very similar to galactose which is the immunodominant (terminal sugar) for the B antigen.

Question 9

How would you resolve a type where the antigens in the front type are not demonstrating?

Answer 9

Incubate the front type at room temperature for 15-30 minutes. If there is still no reaction incubate the front type at 4C for 15-30 minutes.

Question 10

What is rouleaux?

Answer 10

Stacking of RBCs in a coin-like fashion that mimics agglutination. This is not true agglutination, instead the cells are sticking together due to protein abnormalities.

Question 11

List 4 reasons that would cause a patient to have rouleaux.

Answer 11

Multiple myeloma, Waldenstrom’s macroglobulinemia

Question 12

How would you resolve a back type where rouleaux is interfering?

Answer 12

Perform a saline replacement: replace plasma with 2 drops of saline and respin. If it is still positive then the agglutination is true agglutination. If it is negative, then the agglutination was due to rouleaux.

Question 13

If a patient has a cold autoantibody in which part of the type would you expect to see a type discrepancy?

Answer 13

Weaker cold autoantibodies will show only in the back type. Very strong cold autoantibodies may show in both the front and back type.

Question 14

How would you resolve a type where a cold autoantibody is interfering with the back type?

Answer 14

Warm plasma and RBCs to be tested separately for 10-15 minutes. Mix the plasma and red cells together and incubate for 60min. Read the reactions at 37C without spinning.

Question 15

How would you resolve a type where a cold autoantibody is interfering with the front type?

Answer 15

Incubate red cells and saline separately at 37C for 10-15 minutes. Wash the red cells 3-4 times with warm saline. Re-type the patient. If there are still issues treat the cells with DTT (this removed IgM agglutination).

Question 16

If it is believed that a patient has formed an anti-A1 how would we expect their red cells to react when tested with anti-A1 lectin?

Answer 16

If they formed an anti-A1 they should be type A2 or A2B so the reaction with anti-A1 lectin should be negative.

Question 17

Name one alloantibody that has been known to interfere with a patient’s back type?

Answer 17

Anti-M

Question 18

How would you resolve an alloantibody that was demonstrating in the back type?

Answer 18

Either follow the steps for a cold autoantibody or identify the antibody and find A1 and B cells negative for that antibody to use in your back type.

Question 19

List two reasons that a patient’s type may appear mixed field.

Answer 19

Bone Marrow Transplant and transfusion of a different type of red cells

Question 20

What genes will a person inherit if they are Cis-AB?

Answer 20

They inherit both A and B genes from one parent (on one chromosome from unequal crossing over) and an O gene from another parent.

Question 21

What will the reaction look like if an A3 individual’s red cells are tested with Anti-A?

Answer 21

It will be mixed field.

Question 22

The Ax subgroup can sometimes be confused with what other blood type? Why?

Answer 22

Type O. The Anti-A reaction will often be negative and Ax individuals almost always form an anti-A1.

Question 23

How does the Anti-A,B reaction with an Ax individual differ from the Anti-A,B reaction of other A subgroups?

Answer 23

It is the only subgroup that agglutinates very well with Anti-A,B

Question 24

If an individual is typed as the Aend subgroup what reactions would you expect to see with Anti-A and Anti-A,B?

Answer 24

Weak mixed field reactions with both

Question 25

Will the Am subgroup and Ay subgroup form an anti-A1?

Answer 25

No, not usually

Question 26

How do the reactions in blood typing for the Ael subgroup differ from the Am and Ay subgroups?

Answer 26

The Ael subgroup will form an anti-A1 while the other two subgroups will not.