Thermal threshold testing, also known as quantitative or qualitiative sensory testing (I've seen both used), was one of the more prominent tests for determining small-fiber neuropathy problems before skin biopsy was developed.

In essence, electrodes that can assume various temperatures are affixed to body parts, and the patient reports when temperature seems to be increasing/decreasing, when the sensation gets painful, and when a difference is just noticable. In this way, the functioning of the small nerve fibers that subsume the sensations of pain and temperature can be evaluated.

The problems with the testing include wide individual variation in the snesory abilities of individuals, which may be natural variations and not indicative of neuropathy, and also the need to rely on the individual reporting of the test subject.

Certainly, this type of testing can indicate neuropathy if there are wide abnormalities of reported sensation, but it is not as exacting as skin biopsy. I had this testing done, and did not have reports outside normal ranges to the changing temperatures, while my skin biopsy rather definitely showed reduced intraepidermal nerve fiber density and damage.