Bouillon et al measured fecal thyroxine levels to identify patients taking oral thyroxine to cause thyrotoxicosis factitia. The authors are from Katholieke Universiteit in Leuven, Belgium.



(1) Weigh an aliquot of feces.

(2) Mix with absolute alcohol in a ratio of 1 g feces to 3 g ethanol (weight for weight). The density of absolute alcohol is 0.789 at room temperature. 3 grams absolute ethanol is 3.8 mL.

(3) Homogenize the mixture and shake for 12 hours.

(4) Centrifuge the sample for 10 minutes at 3,000 rpm.

(5) An aliquot of the supernatant is dried and assayed for l-T4.


The result of the assay is expressed as nmol of thyroxine in per mL supernatant.


concentration of thryoxine in nmol per mL supernatant =

= (nmol per volume supernatant) / (volume of supernatant in mL)


concentration of thyroxine in nmol per gram feces =

= (concentration of thyroxine in nmol per mL supernatant) * (3.8 mL per gram feces)



• A normal person has < 2 nmol T4 per gram feces.

• A person with Graves's disease will have < 5.2 nmol T4 per gram feces.

• A person with thyrotoxicosis factitia will often have values > 10 nmol T4 per gram feces.


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