Back when they first started working on this at Hopkins, the reserachers were looking for a way to set a standard, since the degree of intraepidermal nerve fiber density is very individual, both among those with symptoms and those without, and from one spot on the body to another.

It was finally decided to consider a rather narrow range "abnormal", in order to get a fair degree of certainty that neuropathic damage actually existed for those people.

This is initially detailed in:

http://archneur.ama-assn.org/cgi/con...act/55/12/1513

Of course, as I've mentioned, it's possible for one to have small-fiber damage even if one doesn't fall into these rather narrow ranges; it all depends on at what point one started. It is known that intraepidermal nerve fiber density does decrease a bit with age, even in those with no neuropathic symptoms. And, if one starts in the 70th percentile, say, and something happens to reduce that person to the 10th percentile, they would not register as having abnormal density, though they might be greatly symptomatic. This is why a morphological examination of the fibers is also necessary.