The MD's have to test for it, for legal liability reasons. The alternative choice to them testing for it, is for them to not test for it, and just mete out Iodine to people. Eventually, they'd encounter a patient with impaired oxidation pathways who would have a freak-out type reaction, and the MD's would be sued. Essentially, for most times when something is dispensed by a physician, the decision to do so is based on at least one test result. Its just normal protocol. Sometimes the Iodine loading test can reveal problems in a person, which would cause a physician to take a different course than merely prescribing iodine, this is discussed in one of Abraham's papers.
So the test has value and any reasonable physician would order the test for every patient. Its not that expensive.