MTS gel testing - air gap in microtube

[gonneb25]

To all gel users: do you feel it is critical to have the "air gap" in between the cells suspension and the gel media? Some of my techs have been trained that way and are insisting that they see weaker reactions with the QC (expected 2-3+ but only see a w+) if there is no air gap. The directions for the gel cards state " the mixture may or may not touch gel suspension". I have already contacted tech support at Ortho and they are supporting the directions as written and MTS in Florida is also stating that it does not affect testing. What do you think? Do you start over if you see the suspension has gone beyond the "reaction chamber" prior to incubation? Thanks! Barb G.

[calynn]

We use gel for both Types and Screens (several thousand tests/month) and I have never noticed any difference, nor have I had comments/complaints from my other techs. When the Tecan is doing the pipetting, there are not always 'air gaps' and this seems to make no difference as to the outcome.

[S.Hunt]

We have found - GAP or NO GAP - the antibody screen or panel results are the same. When we validated the MTS IgG Gel testing system , there were some techs that were concerned so we ran the testing both ways and found 2 out of 100 that varied. One was a positive antibody screen the was due to an Anti-Jka, Anti-Kell combination and the other was a newly identified Anti-Kell - the maximum reaction difference was fnever a full grade. We do not use the Gel system for ABO/Rh testing. And these results were acceptable to the medical director.

[Walter]

I have seen and experienced weakened reactions in MTS gel tests when I have pipetted cell and plasma straight down into the chamber with the Biohit pipette.

Try this experiment:

Center the tip of the pipette in the chamber opening.

Pipet screening cells vertically into a gel tube chamber with enough force to eliminate the air-gap over the gel.

Then, in the same manner, pipette QC material (dilute anti-D or other dilute antibody) into the cells.

Do the same in the adjacent gel tube pipetting at and angle, preserving the air-gap.

Mark each tube accordingly. Continue setting up tubes until two cards have been prepared.

Incubate, spin and compare reactions.

Walter

[Shannon]

The only difference in strength we have seen is when we convert 3-5% cells to .8%. These show an obvious increase in stsrength. (very helpful with weak Ab's) We also have encountered several fairly strong Ab's in PEG that are negative in Gel.

[Diane]

We were taught when trained on the Ortho gel, that it is OK if the cell suspension goes into the neck of the gel tube, but to remember that if there is a reaction in that tube, you might see a mixed cell picture, since some of the red cells would not have incubated with the pt plasma & would therefore go to the bottom of the gel.

Our trainor did NOT address when I manage occasionally to shoot the plasma past the cells & into the neck of the tube. I have decided that, since there is such a tiny volume of plasma, this is NOT OK. It would mean that most of the cells did not incubate with the plasma.

[kelliott]

We have been using the system for 10 years. After our initial training we were ready to send the equipment back - it was not performing as well as our PeG tube method. Another trainer came and informed us that we were losing sensitivity when all of the reactants did not remain in the reaction chamber during incubation (in other words - there must be an air gap). After that the sensitivity met our standards. If you don't have an airgap you will miss a weak antibody (antibody reacting 1+ or less). When we have a miss pipette (the cells touch the gel column we reset the test).