Credibility of hair densitometry/densitometer (for genetic male hair loss)?

I went to see a hair restoration doc one time who used a densitometer to measure the density of my hairs and ured me that I exhibited very early signs of hair thinning and some loss. He put me on propecia but the question is...the derm/trichologist/physians that I have seen have never heard of densitometry, one derm knew but he told me that it is only an art and is not to be completely trusted. He ured me that we all lose hair density as we grow older and just because we lose some hair density and some miniaturization but it does not mean we should take propecia especially since he thought my hair density was normal and I had a full head of thick hair still. He felt I should take it when I exhibit observable loss. It seems these derms don't really buy into the art of hair densitometry. Have you ever heard of this densitometer/densitometry? Would you trust it or should I just follow the derm's advice. I'm 26 and I still have a full head of hair just a little thin on the sides