Genotype AB only reacting with anti-A

[catm]

We have a patient with an anomalous ABO group. Serologically the forward group looks like an A but there is no reaction with A or B cells in the reverse group. We did the tests using Ortho, BioRad and 4°C tube. All tests results were the same so we did the genotype and it grouped as an AB using an Inno-Train kit . Does anyone have an explanation for this?

[galvania]

Possibilities:

1. A very weak subgroup of B. Full genotyping should show if the B gene is normal.

2. Something is blocking the translation of a normal B gene into a normal B antigen. (At the transferase level, probably. If it were the H then the A would be affected too.

3. Both the B gene and the B antigen are normal but something in the plasma is blocking the reaction between the B antigen and the anti-B.

4. A cis-AB where the B is very abnormal. Knowing the parent's groups might solve that one.

5. A leukaemia or similar that has knocked out the B antigen, hopefully temporarily.

6. (And this would be my favorite). Post bone marrow transplant A to AB

7. A newborn whose A has developed but not yet his B

I'm sure Malcolm will find some other possibilities that I haven't thought of.

Try washing the cells really well then repeat the antigen testing in tube at 4°C using an excess of anti-B (human if possible). You could try an adsorption-elution as well

[Malcolm Needs ☆]

It could just be that, as there is competition between the 3-N-alpha-D-acetylgalactosyl transferase and the 3-N-alpha-D-galactosyl transferase (these enzymes are the actual gene product, rather than the A or B antigen), that there is either a mutation in the latter (as Anna suggests), or that it is just that the former is winning hands down!

[catm]

Thank you for your replies. My next question is which ABO group would you transfuse? At present there is no blood requirement but we have recommended low titre group O until we have a satisfactory explanation of the serological results

[Malcolm Needs ☆]

With ABO, I would ALWAYS err on the side of safety, and give group O, low titer anti-A and anti-B (anti-AB) in this case.

[Malcolm Needs ☆]

Hm, that makes it sound like I wouldn't err on the side of safety for other blood groups, but that isn't what I meant!!!!!!!!!