How do you decide when to evaluate for central hypothyroidism in a patient with low-normal TSH and low free T4?

The differential in these patients is 1)mild subclinical hyperthyroidism 2)central hypothyroidism 3)normal variant related to assay detection limitations.

It would be important to obtain a good history and try to identify if any hypothyroid or hyperthyroid symptoms. Having said that patients will usu...