Prewarm for a positive D control

[Blood Bank student 1]

Hi,

We had a grouping discrepancy for a patient where forward group reactions were all positive including the Rh control.

Patient's original group was A positive but we had weak reactions with Anti-A and A1 cells.

(washed patient cells 4 times with RT saline and repeated group, same reactions)

The antibody screen was positive including the autocontrol. Dat and eluate all positive. So we thought it's a warm auto and send it to our reference lab for investigation.

They performed adsorption with zzap'd cells and there was no clinically significant antibody detected in adsorbed plasma.

To resolve the grouping discrepancy they used prewarm technique and got a valid ABO.

My question is about the use of this pre-warming technique to resolve the grouping discrepancy. Was it appropriate to resolve the group without proving the presence of a cold antibody?

Thank you

 

[exlimey 378]

15 hours ago, Blood Bank student said:

Hi,

We had a grouping discrepancy for a patient where forward group reactions were all positive including the Rh control.

Patient's original group was A positive but we had weak reactions with Anti-A and A1 cells.

(washed patient cells 4 times with RT saline and repeated group, same reactions)

The antibody screen was positive including the autocontrol. Dat and eluate all positive. So we thought it's a warm auto and send it to our reference lab for investigation.

They performed adsorption with zzap'd cells and there was no clinically significant antibody detected in adsorbed plasma.

To resolve the grouping discrepancy they used prewarm technique and got a valid ABO.

My question is about the use of this pre-warming technique to resolve the grouping discrepancy. Was it appropriate to resolve the group without proving the presence of a cold antibody?

Thank you

 

Arguably the initial ABO discrepancy is proof of the presence of a cold-reactive antibody.

If the DAT was positive, how do you determine that the autocontrol is valid ? Surely its just the same DAT-positive cells reacting with the antiglobulin reagent, or were the patient's cells treated to render them DAT-negative prior to testing ?

Were the "zzap'd cells" autologous ?

[Blood Bank student 1]

Thank you for the reply.

The ZZAP'd cells were allogenic.

At our institute if the DC is positive and the DAT is also positive due to IgG. We ZZAP the patient's cells and repeat Rh group.

I was surprised the IRL did not do that.

[exlimey 378]

Tests on the adsorbed serum (with ZZAP-treated cells) give confidence that the are no underlying alloantibodies to common antigens. However, the use of allogeneic cells risks removal of a cold-reactive alloantibody to a high incidence antigen, e.g. anti-Vel, -PP1pK. A low risk, but still concerning.

Does you facility also test the ZZAP-treated patient cells (now presumably DAT-negative) back against the patient's own serum ? This is ultimate proof that the cold-reactive antibody is an AUTOantibody and adds more confidence in the results of the adsorption with allogenic cells.

I may be opening a can of worms here, but.....I question the use of ZZAP in this scenario. In this case, the adsorption used (presumably DAT-negative) allogenic cells. ZZAP was not required to "reduce the DAT and enhance antibody uptake" - which is a true statement about performing AUTOadsorptions with DAT-positive cells. I appreciate that the enzyme in ZZAP enhances the efficiency of the adsorption, but the DTT component is not necessary for most alloadsorptions, and can actually confuse the users. I suspect the answer/policy is related to ZZAP being commercially available, rather than in a well-founded technical reason.

[Joanne P. Scannell 219]

We have found that washing the cells 3x with 37C saline will resolve this situation in just about every case where RT Saline wash doesn't help.

If you are using Gel, there may be other reasons for the extraneous 'positive results' using your patient cells, e.g. sickled cells, acanthrocytes, protein coating.  So, those must also be considered.