How often do you recommend we re-test blood markers and re-do the hair test?

That's really up to you and how much you can afford to run these tests regularly. But I would say it's good to check TSH, T3, T4 and Ferritin every 6-8 weeks if possible. But it definitely doesn't have to be that often. It's completely up to you.

For the hair test, since it's not that expensive, I would say maybe once every 4 months. Some people just get it done once every 6 months. So again, it's really up to you. 

You also have to keep in mind that the hair you're cutting off your head will show the status of iodine and selenium from about 3 months ago. Because it takes some time for your hair to grow, right? So it's not showing your current status from the exact day you cut off your hair. Rather, it's showing your iodine and selenium status from about 3 months ago, depending on how quickly your hair grows. So there's no need to really get that test done too often because you won't see much of a change.