Hello & welcome to Just Answer! If you have any questions after reading my answer, be sure to let me know.
If you do have Lupus it is possible that sun exposure may increase your titres slightly, but the effect is variable, and is unlikely to cause a false positive (means that it is not going to wrongly diagnose you as a case of Lupus, just because you have been exposed to the sun)
Of course sitting in the sun may cause LUPUS to flare up, and hence this is NOT a good idea without the all clear from your doctor
There are other tests like ESR and CRP that would help in diagnosing an auto-immune condition too,
Please leave a positive feedback, get back for any clarifications
Thank you for your feedback. :) The reason I asked that question is because my doctor ordered an ANA test for me, but it came back negative. (My C3 was low, however.) I was really surprised by the result, because I have many symptoms related to Lupus. I just can't help but wonder...if I'd had my blood drawn mid-day after I'd been in the sun for a little while, because that's when I'm most symptomatic, would my ANA results have been any different. Instead I had my blood drawn in the morning when I'm least symptomatic. Do you think it might be beneficial to get retested during mid-day? I want to talk to my doctor about this possibility, but I'm afraid she'll think it's just plain nonsense to even ask to be retested. What do you think?