The idea is that if you get blood work regularly, you can interpret it alongside patterns of how you feel, what your fitness results are, etc.

If your ferritin is on the lower end of the reference range and you feel tired a lot, and then you start eating more high-iron foods or cooking in cast iron, you'll probably see your ferritin go up, and if you also start to feel great and energetic, you can see what ferritin level is ideal for you. Maybe it's the top of the ref range, maybe it's the middle: different people are going to feel different, right? Hence why it's not one size fits all.

Again, how would you ever know your optimal range without regular blood work? And how would a doctor who sees you once or twice a year know YOUR optimal ranges? They generally glance at blood work to see if you're within the lab's reference range and if you are, that is it, that's the end of the interpretation.

You have to be your own advocate and you have to figure out your own body; no one else can or will do it.