A Serological Problem from the SBB Exam

[cbaldwin]

I just took (and passed!) the SBB exam.

 

There were several questions on the exam I wondered about, here is one.  Any ideas on what is going on here?

 

1. This is a serological problem, in which anti-Fy^a is adsorbed onto cells and the eluate is tested.  The results are compared to an eluate made from Fy(a+) cells that were also incubated with anti-Fy^a.  I don’t remember all the details but this is my best:

 

Patient cells/anti-Fy^a eluate tested with patient cells:  3+

Patient cells/anti-Fy^a eluate tested with Fy(a+b-) cells:  0

Patient cells/anti-Fy^a eluate tested with Fy(a+b+) cells:  0

Patient cells/anti-Fy^a eluate tested with Fy(a-b-) cells:  0

 

Fy(a+) cells/anti-Fy^a eluate tested with patient cells:  0

Fy(a+) cells/anti-Fy^a eluate tested with Fy(a+b-) cells:  3+

Fy(a+) cells/anti-Fy^a eluate tested with Fy(a+b+) cells:  3+

Fy(a+) cells/anti-Fy^a eluate tested with Fy(a-b-) cells:  0

 

The question asked was whether Fy^a was present or not, or if you needed more information.  I said that Fy^a was not present, but I wasn't sure. 

 

Why is the eluate from the anti-Fy^a/patient cells reacting with the patient cells?  I think there is something other than anti-Fy^a on the cells that ends up in the eluate, and when tested with patient cells, it, of course, reacts with them.  Or is something more complex going on?

[Malcolm Needs ☆]

First of all, heartiest congratulations on passing your exam.

 

I think that that the patient is Fy(a-).

 

I also think, however, that the anti-Fya also contains another antibody, probably directed against a low prevalence antigen, which is expressed on the patient's red cells, but not expressed on the Fy(a+b-), the Fy(a+b+) or the Fy(a-b-) reagent red cells.

 

Hence, when the elution is performed, the eluate reacts with the patient's red cells, but not the Fy(a+b-) or Fy(a+b+) reagent red cells.

 

Did I pass?

[David Saikin]

Sounds reasonable to me Malcolm.  I was glad that I was the last group to have the SBB practical exam rather than the "serological questions".  I agree that the patient does not appear to be Fya+.  I really dislike these "theoretical" exercises. 

 

Also my congrats on passing the exam.

[tbostock]

Yeah, what Malcolm said!

Congrats on passing your exam...that is quite the accomplishment!!!

[L106]

Congratulations on your success!!

 

Donna

[Dr. Pepper]

Congratulations and ditto on the extra antibody in there.

 

I think David and I were in the same "class". We had some theoretical questions, which, although they turned out not to be graded, were a trial for dropping the wet exam. I agree, they're fiendish, especially when you're not supposed to go back and revise your answers based on new evidence from a few questions down the road.

[David Saikin]

.

 

I think David and I were in the same "class". We had some theoretical questions, which, although they turned out not to be graded, were a trial for dropping the wet exam. I agree, they're fiendish, especially when you're not supposed to go back and revise your answers based on new evidence from a few questions down the road.

You must be right on this - I remember those questions vividly and was very pleased that they would not be graded.

[aafrin]

Congratulations on your success!

[Eagle Eye]

Congratulation on passing SBB exam.....Excellent.

 

Join the group of >6000 SBB.....It depends on your license number. When I took mine in 2006, my number is in upper 4000 almost close to 5000.

They were >6000 last year so I do not know how many more SBB added to the list. I do not think they have that many SBB(ASCP).

 

You are the Best Malcolm.

[AMcCord]

Gold Star +++ for you!

[ckcheng]

Agree with Malcolm, also think the patient is Fy(a-).