The physiology of the thyroid gland is truly remarkable — both simple and complex, yet very elegant. In medical school, students are taught all about thyroid physiology.

Then they are tested on it, inside and out. And then a funny thing happens . . .

When they move from the book years of medical school to the clinical training years in residency, young doctors basically turn into apprentices.

They follow more senior physicians in order to watch and learn how to treat patients.

There is a hierarchy at work: The most senior attending physician is over the senior resident who watches over the junior residents who watch over medical students.

During my clinical training, endocrinologists taught us that to properly evaluate the thyroid gland, a doctor needed only to order a thyroid stimulating hormone (TSH) test.

If the results of that single test fell within what we call the “reference range,” there was believed to be no issue with the patient’s thyroid gland.

I vividly remember asking one endocrinologist why he didn’t test for T3 and T4 along with TSH. He said it was a waste of money. “TSH is the only test that you need.”

When I told him that some of the older doctors were, in fact, testing T3 and T4 levels, he said, “They’re quacks.” At that point, I stopped asking questions.

Now that doctor would refer to me as a “quack.” But I am happy to keep on quacking and diagnosing and treating thyroid problems.