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Levothyroxine Absorption Test to Differentiate Pseudomalabsorption from True Malabsorption
Author(s) -
Sujoy Ghosh,
Subhodip Pramanik,
Kaushik Biswas,
Kingshuk Bhattacharjee,
Rajib Sarkar,
Subhankar Chowdhury,
Pradip Mukhopadhyay
Publication year - 2019
Publication title -
european thyroid journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.23
H-Index - 10
eISSN - 2235-0802
pISSN - 2235-0640
DOI - 10.1159/000504218
Subject(s) - levothyroxine , malabsorption , medicine , euthyroid , gastroenterology , endocrinology , intestinal malabsorption , hormone , coeliac disease , disease
Background: The levothyroxine absorption test for evaluation of pseudomalabsorption in patients with primary hypothyroid is not standardised. An individual in whom a workup for malabsorption is warranted remains undefined. Methods: Twenty-five euthyroid, 25 newly diagnosed hypothyroid, 25 treated hypothyroid with normalised TSH, and 25 hypothyroid subjects with elevated TSH despite adequate dose of levothyroxine for more than 6 months, and 10 euthyroid subjects with true malabsorption were administered levothyroxine (10 μg/kg or maximum 600 μg) to study its absorption profile by measuring free T4 level at hourly intervals for 5 h. Results: Free T4 peaked at 3 h with marginal insignificant decline at 4 h in all groups. The increments of free T4 (between baseline and 3 h) of the four groups (except malabsorption) were not statistically different. The mean increment of free T4 in true malabsorption was 0.39 ng/dL (95% CI: 0.29–0.52) and it was 0.78 ng/dL (95% CI: 0.73–0.85) (10.4 pmol/L) for other groups combined together. The cut off of free T4 increment at 3 h from baseline above 0.40 ng/dL had a sensitivity of 97% and specificity of 80% (AUC 0.904, p < 0.001) to exclude true malabsorption. Conclusion: Subjects with elevated TSH on adequate dose of LT4 can be reliably diagnosed to be non-adherent to treatment with levothyroxine absorption test. The incremental value above 0.40 ng/dL (5.14 pmol/L) at 3 h may be useful to identify individuals where workup of malabsorption is unwarranted.

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