Noooooodles

If there ARE extra reactions in the back type, then they do need to be resolved IF, and I mean IF, they look as if they could signify that the forward ABO type is false.  That having been said, I STILL would not go looking for rouleaux or agglutination that was not present when the tests are read at their normal incubation period and temperature.  Why would you want to look for a herd of Zebra, when you hear a herd of Horses (thank you John C Staley - or, at least, I think it was you who used to say this to me on a regular basis - apologies if it was not - but it was a great comment!)?

I went back to your original post and it clearly said "Trigger" for some posters.  My lab only uses the microscope for FMH screening tests and rarely (like once in a blue moon) looking for mixed field during post-transfusion reaction investigations.  I would consider it to be looking for Zebras, as Malcom said, to want to see rouleaux or a cold-reactive antibody by letting tubes "sit before looking under the microscope" (slightly adulterated version, my apologies).  I didn't see any mention of "only for ABO discrepancies" or even "reverse type".
I've seen cold reactive antibodies look like rouleaux and rouleaux that gave the same appearance as cold reactive antibodies. Some are helped to be clearer with saline replacement, some not.  That's probably where I stopped looking at these things under a microscope.  We predominantly test using automated gel method with tube usually being the "come to the rescue" method to not see just those things you were talking about.  Do I saline replace or pre-warm the test components for those things?  If I need to, but I try not to wake the sleeping beasts so I don't see them in the first place.

It's cause our contract is coming up and we can't find another solid phase instrument for our sample volume. Much more choices with gel instruments.