Levothyroxine Absorption Test - Results and Follow Up of Patients from a Single Center

Treating primary hypothyroidism with appropriate weight-based dosing is usually straightforward. When supraphysiologic doses of thyroxine are required, it is important to know the reason behind the increased requirement. When compliance with medication is assured and when there are no drug interactions resulting in increased thyroxine requirements, a levothyroxine absorption test (LT4AT) could be performed to diagnose the coexistence of malabsorption.

This was a single-center, retrospective chart review. Patients who had undergone LT4AT between 2018 and 2020 with a complete evaluation and follow-up records were reviewed. LT4AT and further evaluation (if necessary) were standardized, and details until the last review were obtained.

In all, 11 patients had complete records and follow-up details. The median age (range) of the cohort was 24 years (19 to 46), and the duration of hypothyroidism was 8 years (4 to 24). Seven had low absorption (<60%) in LT4AT of which two each had celiac disease and Helicobacter pylori infection; one had autoimmune gastritis, and in two the reasons of malabsorption was not known. The median follow-up duration was 13 months. Nine of 11 (81%) achieved euthyroid state with/without thyroxine dose reduction on follow-up.

A high proportion of patients requiring supraphysiological doses of levothyroxine had occult malabsorptive states, some of which were curable. Even in those with pseudo-malabsorption, LT4AT helped in reinforcing compliance and thereby thyroxine dose reduction.