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Eur J Endocrinol. 2013 May 10;168(6):913-7. doi: 10.1530/EJE-12-1035. Print 2013 Jun.

A thyroxine absorption test followed by weekly thyroxine administration: a method to assess non-adherence to treatment.

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  • 1Department of Endocrinology, Oxford University Hospitals NHS Trust, OCDEM, Oxford OX3 7LJ, UK.



For patients who remain hypothyroid despite the administration of what would seem adequate doses of levothyroxine (L-T4), the underlying cause can be difficult to determine. The possibility of a biological cause should first be explored; however, in the majority of cases, poor adherence to medication is likely to be the main cause of treatment failure. When non-adherence is suspected but not volunteered, options to confirm the suspicion are limited. In this study, we identified patients for whom known drugs and pathological causes of L-T4 malabsorption were excluded, and despite often high doses of L-T4, the patients remained hypothyroid.


Using a weight-determined oral L-T4 bolus administration, absorption was initially assessed in 23 patients. In nearly all patients, this was shown to be maximal at 120 min post-ingestion. This was then followed by the continued administration of a weekly T4 bolus for a 4-week period after which TSH and free T4 (fT4) levels were recorded.


All patients showed a rise in fT4 at 120 min following the administration of the L-T4 bolus, with a mean increase of 54±3% from baseline. Following the treatment period, using an equivalent weekly L-T4 dose, which was significantly less than that of the daily dose taken by the patients before the test, TSH reduced from baseline in ~75% of cases.


Using this combination of tests allows significant malabsorptive problems to be identified first and then potential non-adherence to be demonstrated. A management plan can then be implemented to increase adherence, aiming to improve treatment outcomes.

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