I can see on the other thread that some are recommending applying iodine to skin and checking for absorption. There appears to be quite a bit of confusion on this test and it seems like the test itself is meaningless.
Basically speaking, most of the iodine simply evaporates.
This really leaves a more simple question, how does one actually test for iodine content?
Here is an article on the matter:
The bioavailability of iodine applied to the skin