I have both a limited FSA and an HSA to go with my HDHP at work. The limited FSA works like an FSA but is only eligible for dental, vision, and preventative care expenses, which includes diagnostic. However, I haven't been able to find any definitive IRS information about what "diagnostic" means. (Or maybe my Google skills just need work. Always a possibility.)
In my case, for example, I have a chronic medical condition that is right now still in its latent stage and thus is being untreated. However, I have to get regular labwork done to make sure it's still sleeping, so to speak. When I get my EOBs, these labs say "diagnostic."
Some things I found online say that as long as it's not for something that's being treated, then it's covered under that diagnostic/preventative care umbrella. Other sources say no. I'm not sure how to interpret this rule myself; on the one hand, I already HAVE an official diagnosis so there's nothing to prevent anymore, but on the other hand, I don't have the symptoms yet, I'm not getting treatment, and though it's chronic, it's inactive. We're just keeping an eye on the sleeping monster.
I'd much rather pay for these labs with my limited FSA than to touch my HSA, especially because I'm going to have to endure a lifetime of these so-called diagnostic labs and I'd like to stretch my tax-protected medical funds as much as possible.
Has anyone had any experience with limited FSAs, or know how the IRS considers what is preventative/diagnostic?