
I'd check with your vet but that's my understanding of steroids on several types of blood tests. The thing is, the fact he's now on a course of them means that re-doing any tests already carried out will again affect readings.
There will be other things which cause symptoms similar to Addisons but of course your vet has the benefit of expertise in what many are and how likely any are. Do you know if s/he tested for and ruled out any other specific diseases such as SIBO, giardia, pancreatic problems, IBD? (guessing here as I'm assuming from Addisons cropping up the symptoms are pointing to severe GI problems - which may not be the entire picture)