I mostly agree with Trapper, i think everyone needs to take iodine, but I believe the testing can be useful for some folks for several reasons:
1. The loading test can indicate a possible transport problem:
If the Iodine loading test shows near to 90% excretion, which the test designers say indicates tissue saturation yet you are taking relatively little Iodine in your diet, you are probably peeing it all out because your cells can't absorb it. This could be a symporter (NIS--Sodium Iodide Symporter) problem. Or, this could be an organification problem. Or both.
2. The serum/saliva test can more clearly show transport issues:
This is a more specific test which involves looking at levels or Iodine in both the serum (blood) and the saliva (can the iodine get into the tissues) and creating a ratio between the two. A low ratio implies symporter issue and a high ratio implies organification/oxidation issue.
so way is it important to identify a possible transport problem? Because you can fix a symporter problem faster by taking sufficient amounts of antioxidants.
So while I hear your desire to get your nutrients through your food, sometimes it can be useful to put your Linus Pauling hat on give your body the protection it needs (>= 3g of vitamin C, etc) to deal with the all the "unnatural" crap that the iodine is kicking out of your body.
You can also fix an organification/oxidation problem by taking adequate amounts of B2/B3, larger than you can find in most b-complex supplements. This is something that doesn't get a lot of play on this forum, but for some people can be a big deal.
In Brownsteins book he mentions a patient who barely noticed any positive changes after several months on 50mg Iodoral per day. He added B2/B3 supplements and immediately the patient noticed improvements.
3. You may have high amounts of bromide interfering with iodine uptake:
I always recommend clients test their bromide levels at the same time they do their loading test. If your bromide is high it can mess everything up regarding Iodine utilization. AND IMHO it can be useful to retest just the bromide 6 months or one year later. Mine is still high after 1 1/2 years on 100+mg Iodine/day. This gives me reason to keep taking the iodine for as long as it takes to get the bromide level down. I say this because I have watched a number of people in my life, start the iodine and if they don't notice anything they get bored and let it go, thinking that they have done that experiment and it wasn't that important for them.
I saw Dr Brownstein speak in Boulder Colorado in 2007 and he said that it took him 4 years on 50mg iodoral/day before his Bromide levels dropped to a reasonable level.
so, to test or not to test.
For some people testing isn't that important....maybe a woman has fibrous breasts so she knows she has to take iodine until her breasts change. The course is clear for the most part. But in a complex case like mine with multiple variables I find it helpful to keep my focus. For others it can be helpful to make sure they are taking the necessary additional supplements to make sure they are healing transport issues.
And as far as skin painting goes, there are too many variables for this test to be useful from everything I have read: humidity, skin absorption variability, atmospheric pressure, etc.