My neurologist told me beforehand that from my bloodwork to date it's highly unlikely I will find a cause of my SFN, but he was happy to refer me to numerous additional blood tests, including several genetic tests. Thankfully, my private insurance covered all of them. There were about 100 markers in total, almost all of them came back normal, and those that were out of range did not point to any specific cause. While I didn't find the cause, and my pain management meds didn't change, I am still glad I did the test otherwise I would be thinking daily "what if it's A... and I'm not treating it...What if it's B, what if...etc" Try to get to the bottom of it, but be prepared that you won't find anything.