Well if we’re following the lead of how endocrinologists manage dosing, Z is used to “get in the normal IGF range” and manage safety by not exceeding 2. For us, up to 3 is most likely safe long term (endos, like with TRT, are much more conservative).
But within that range, the other things that guide dose are side effects and results.
(Using made up numbers for this example).
If Z 1.5 gives you sides that don’t diminish in a few weeks obviously going to 2.5 isn’t gonna to help. Z allows you to figure out “I need to be at 1 to 1.25 z score to feel best without sides” rather than IU which can be very inaccurate, changing from batch to batch. There’s also changes in your biology that could raise or lower IGF/Z score on the same dose, so again, Z score as your guide gives you a way of tweaking the dose to get the results you want.
One other thing, if you have a choice, get IGF tested at Quest not Labcorp. This may apply to you specifically.
I just encountered a situation where Labcorp was giving a crazy low IGF-1 (50), so he kept on increasing rHGH doses, up to 15iu/day, to try and normalize IGF. 15iu only got him to IGF -1 80.
After switching to Quest, IGF was actually 650, far into acromegaly levels!!
It’s something that’s rare, probably less than 1% of people could have this issue, but the consequences could be bad for those of us using levels of rHGH no endo would ever use regardless of IGF.
Labcorp uses a bioassay, Quest uses LCMS. LCMS sees things bioassays miss.