The symptoms and signs of hyper- and hypothyroidism are well known to primary care clinicians. When either diagnosis is suspected, the usual next step is to order blood tests to determine whether the clinical impression of thyroid disease can be confirmed.

Generally speaking, only a single blood test is needed as the initial screen. Most of the time, it is not necessary to simultaneously order a TSH and a free T4. In the old days, the TSH assay was less accurate. It was useful in diagnosing hypothyroidism, but was not accurate for diagnosing hyperthyroidism. So ordering a free T4 along with the TSH was fairly common. But today’s TSH is not your grandparents’ TSH. It is more sophisticated and can accurately point to hyperthyroidism as well as hypothyroidism. The only situation where one might order both a TSH and a free T4 simultaneously is when suspecting hypothalamic or pituitary disease. Otherwise, the TSH by itself should tell the tale.

If the TSH is too low, it is appropriate to then check a free T4 and a T3 level. Most labs, including Quest, accept orders for “TSH with reflex to T4.” By ordering this test, if the TSH is abnormal, a free T4 will automatically be done on the same specimen. This saves the patient from having to return to the lab for a second lab draw. And it saves the clinician from needing to order a free T4 at the same time as a TSH when screening for thyroid disease. In a similar vein, the American Society of Clinical Endocrinologists says the only test one needs to follow when treating hypothyroidism is the TSH. If the TSH is in the normal range, the thyroid supplementation dose is correct.

Reducing the ordering of unnecessary free T4 tests will not compromise a patient’s care. And it will not solve the larger problem of health care spending. But each action we take helps. One small step for the physician, one significant step for humankind.

Richard Fleming, MD