Does anybody know what these tests are for?

[chatenoire]

Dermatology is testing for autoimmune conditions that could give me the symptoms I'm experiencing. I'm already iron deficient and hypothyroid so I know what a few of those are for.

They are mostly checking for vitamin/mineral deficiencies, plus coeliac’s, your thyroid and IgA, which is a very broad marker of inflammation, I think often very generally related to skin and digestive tract (for example, mine was high when I was being investigated for a GI condition that causes bowel inflammation). The Hep B&C and HIV are very likely thrown in for good measure if you haven’t been tested much or at all as an adult, but likely don’t have anything to do with your symptoms, just covering all bases.

tTG is testing for Coeliac Disease. IgA is usually treated for at the same time as if you are deficit in that then it can cause a false negative result for Coeliac Disease. There's a related skin condition called Dermatitis Herpetiformis, if that is relevant to your skin symptoms.
https://www.coeliac.org.uk/information-and-support/coeliac-disease/dermatitis-herpetiformis/
https://www.coeliac.org.uk/information-and-support/coeliac-disease/