The symptoms are not subjective, and I wouldn't say it's entirely subjective. We have diagnostic criteria that are based on symptoms and have evolved over time.
We don't have objective markers. We don't have a test, and those markers aren't necessarily limited to diagnosis. They're limited to even prognosis. For example, in certain neurological conditions and cancers, we can prognosticate more definitely on who's going to respond to what treatment and for how long and what their duration of illness might be.