This question came to mind after reading this article. The article speaks of inducing sweating to determine, by a roundabout fashion, the amount of salt therein. I'm no medic but I find myself wondering whether sweat may be used directly to measure any other chemicals secreted by the body.
If one's kidney/liver were to suffer some malady would the body attempt to discharge some additional waste through one's sweat
What chemicals may be detected by analysing sweat?