Tetracycline and Thyroid Function

To the Editor:—  The authors of "Tetracycline and Thyroid Function" have based their conclusions mainly on protein-bound iodine (PBI) and cholesterol levels (199: 416, 1967). Personal experience has led me to conclude that PBI studies are not entirely reliable because of the ease with which alterations in value can occur, as is known to every laboratory technologist. Cholesterol determinations are more valuable when they are performed with a simultaneous study of the cholesterol esters. The percentage evaluation between the two is a more effective determinant of physiological alterations than evaluation of cholesterol alone. As to the comparative Achilles tendon reflex, one must be a little cautious before accentuating its definitive value. There are many subclinical neuromuscular disorders which are overlooked very easily, and these incipient pathological entities may lull the examiner into a false state of security which may cause one to indict the thyroid gland for a physical sign