higher without noun ok?

No you don't. Good as it is.

I would say yes, you do need 'doses' after higher.....not because as it stands it is without meaning, but it suggests there may be a typo involving a missing word/phrase other than 'doses' ( e.g. 'blood pressure').
The fact that you asked the question implies you suspect this might be the case.

That potential ambiguity can be resolved with punctuation.

the orbital fibroblasts of a Graves' ophthalmopathy patient had RARα gene expression, which was not affected by higher, but decreased with lower, doses of glucocorticoids.

Why even mention the "higher dose"?

the orbital fibroblasts of a Graves' ophthalmopathy patient had RARα gene expression, which was decreased with lower doses of glucocorticoids.

The sentence conveys information about the results of higher doses (no effect on RARα gene expression), and lower (decrease of RARα gene expression). We are asked to advise about repetition of the word 'doses', not to alter the meaning.

I try not to change the text too much (I'm a translator) so I don't have to waste time explaining the changes I made.

No need to add doses after higher.

You can put doses after 'higher' and leave it off lower if you have to leave it off one or the other.