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.

IFA better: For a screen the ifa is much better. It is the gold standard. The ANA choice is not a screening test and should not be offered as a screening test. Your question is somewhat counter intuitive. The ifa is a better test and if choice is positive - it can be subseted into 12 antigens and the lab can tell you. I would follow your test results with ANA subsets per your rheumatologist.

Different methods: Different methods of doing a lab test will some times give different results. If one of the tests is negative, it is unlikely that you are at high risk of having a disease associated with anti-nuclear antibodies. It would be prudent to repeat the test in about a year, especially if you continue to have symptoms that prompted the test in the first place.

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).