Is the full crossmatch valid after saline replacement

[Clarest]

Hi all,

We have a patient with strong rouleaux and an alloantibody. According to our policy, we need to perform a full crossmatch which means the crossmatch is carried from immediate spin, to 37C and to AHG phases. Due to the strong rouleaux, a saline replacement technique has to be used during the immediate spin crossmatch phase. I am wondering if the 37C and AHG crossmatch tests can be continued on the tube that has been done with the saline replacement.

Thank you,

Clarest

 

[Malcolm Needs ☆]

The sensitisation stage of antibody/antigen reactions follows the Law of Mass Action.  The rate constants for the forward and reverse reactions will change both with the temperature of incubation, and also with the concentration of the antibody and antigen (amongst other things) and this will, in turn, alter the equilibrium constant of the reaction (which, in the cross-match, you want to drive to the right, but not so much that you will get "false positive" reactions).  You would be ill advised, therefore, to carry on the tests at 37^oc and AHG after saline replacement, as there is every chance that the equilibrium constant would be altered to such an extent that some antibodies would not be detected in vitro, that may be clinically significant in vivo.

[rhesuspieces]

I would set up another tube, concurrently, for the 37 and AHG reactions.  

[knelson]

We do the saline replacement after the tubes have been incubated at 37C, just prior to washing.

[carolyn swickard]

20 hours ago, rhesuspieces said:

I would set up another tube, concurrently, for the 37 and AHG reactions.  

This is the way to go, because otherwise - as you correctly suspected - the 37C and AHG phases have no exposure to the plasma/serum with the alloantibody.  you would have replaced it with non-reactive (one hopes) saline.

[Malcolm Needs ☆]

1 hour ago, knelson said:

We do the saline replacement after the tubes have been incubated at 37C, just prior to washing.

That would be fine.

[David Saikin]

22 hours ago, rhesuspieces said:

I would set up another tube, concurrently, for the 37 and AHG reactions.  

I agree with this.  YOu may see rouleaux again at 37.  You can do saline replacement after this phase and then go directly to wash and ahg phases.

[Clarest]

Thank you all for your replies. They're really helpful.