And to add I do not have any thyroid TT done 20 years ago. But never after that did US to confirm no activity,, I was told that I might had minor thyrosis since I did not take any meds for 15 of those years and had no symptoms. And now what little glad might be left have reactivated and cause for lower dose now. I was up to 200 Synthrod at on time and worked my way back down to this 100 levoxyl now My TSH one year ago was 118 on no meds, but told my TSH 18 years ago was 300, so it came down with no meds. Just started back taking last year.
While this is reported in the handout on HCTZ, there is not much published in the clinical thyroid literature about an effect on thyroid levels and I have not noted in practice that HCTZ alters thyroid levels in any significant way. So it is unclear if it had an effect in your case. An US could be done to see if there is any significant thyroid tissue -- that would not prove it is active tissue, but be a starting point to see how much is there.