LABORATORY PITFALLS IN DIAGNOSIS OF THYROTOXICOSIS

To the Editor:—  The diagnosis of thyrotoxicosis has been facilitated by the determination of the protein bound iodine in the blood and by the uptake of I¹³¹ by the thyroid; however, there are many patients with borderline laboratory results suggestive of thyrotoxicosis but who are clinically not thyrotoxic. This anomaly has been observed in other clinics besides our own. The difficult diagnostic and therapeutic problems presented by these patients directed our attention to a number of factors that must be weighed carefully before final evaluation of the total clinical picture is made. It is felt that unless diagnosis of these borderline cases remains on a clinical level the uncritical physician may attach undue value to an abnormally high basal metabolic rate, high uptake of I¹³¹ by the thyroid, or increased protein bound iodine.False values in protein bound iodine and in the uptake of I¹³¹ are commonly