What is the difference between the anachoice screen and the ANA screen, ifa? The first one came back positve, but the second came back negative.

Diff. lab techniques. Different labs have different ANA tests, which is a test for antibodies a person makes that attach to his own body's tissues, that end up causing auto-immune disease. Modern tests use "reflex" or "cascade" techniques, meaning one test is done first, and then if positive, another test is done, and then if positive again, a third test is done. Tests have various "positive" ranges (gets complicated).