Thyroxine Absorption Test

Khaled Aljenaee¹, Sulaiman Ali², Seong Keat Cheah¹ and John H McDermott¹

Received: March 13, 2018;   Published: March 22, 2018

DOI: 10.26717/BJSTR.2018.03.000881

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Abstract

Poor compliance with Levothyroxine therapy leading to apparently ‘resistant’ hypothyroidism, termed ‘pseudomalabsorption’, is a common clinical conundrum.. A thyroxine absorption test may aid clinicians in confirming suspected poor compliance with greater objectivity, but there is a lack of uniformity in practice and interpretation of this test. We herein report a case of suspected pseudomalabsorption where a thyroxine absorption test helped to confirm the diagnosis. A 29-year-old female was diagnosed with primary hypothyroidism in 2009 with TSH at diagnosis of 180 microIU/L. Euthyroidism was achieved by Levothyroxine administration, which was gradually increased to 175mcg/day. In the subsequent 2 years, however, she remained persistently hypothyroid despite doses of Levothyroxine well exceeding her estimated weight adjusted requirement. A thyroxine absorption test was performed, where once weekly directly observed administration of a weight-adjusted dosage of levothyroxine was performed over a consecutive 4 week period. TSH fell from a baseline of 18 microIU/L to 0.8 microIU/L in the fifth week. This finding confirmed pseudomalabsorption and excluded the need for a potentially exhaustive search for an organic underlying cause for the persistently elevated TSH.

Keywords: Hypothyroidism; Non-compliance; Malabsorption

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