Hi and welcome narges,
As already mentioned, usually a neuro will test for vibration response from the large nerve endings with a tuning fork and a pin prick test for small fibre's for reaction as well, this can be followed by Quanitive Sensory testing, which test for small nerve damage but also measures vibration response as well.
http://millercenter.uchicago.edu/lea...nt/index.shtml,
More tests are usally done,, like a Nerve Conduction test http://www.medicinenet.com/nerve_con...st/article.htm
and or a EMG... http://www.medicinenet.com/electromyogram/article.htm
I was diagnosed as having prediabetes and i had low B12 as well.
What has been done so far ?

Brian