The Measurement of Fecal Thyroxine in the Diagnosis of Thyrotoxicosis Factitia

Abstract

Two patients with prolonged thyrotoxicosis are presented with low radioiodide uptake, low-normal serum thyroglobulin concentrations, and low iodide content of the neck on x-ray fluorescence studies. The surreptitious intake of thyroid hormone was directly proven by a high fecal concentration of T₄ (12.38 and 23.99 nmol/g) compared with low concentrations in healthy subjects (1.03 ± 0.64 nmol/g; mean ± SD, n = 6) and in patients with hyperthyroidism due to Graves' disease (1.93 ± 1.86; n = 8). Fecal thyroid hormone measurement may help to provide formal proof of factitious thyrotoxicosis.