• Mehmet Sözen, Zeynep Canturk, Berrin Cetinarslan, Ilhan Tarkun, Emre Gezer, and Alev Selek.
• Department of Endocrinology and Metabolism, Faculty of Medicine, Kocaeli University, Kocaeli, Turkey.
• J Coll Physicians Surg Pak. 2021 Sep 1; 31 (9): 1099-1101.

AbstractThe levothyroxine absorption test for the assessment of pseudo-malabsorption in patients with refractory hypothyroidism has not been standardised. The aim of this observational study was to describe a protocol for levothyroxine (LT-4) absorption test in patients with refractory hypothyroidism, to report possible side effects and to emphasise the importance of pseudo-malabsorption in the differential diagnosis. The results of 10 patients, who underwent LT-4 absorption tests because thyroid stimulating hormone suppression could not be achieved despite the need for LT-4 >3 mcg/kg/day, were retrospectively analysed. When compared with basal free T4 (fT4), a statistically significant increase in fT4 was observed after the first hour (p=0.012). fT4 reached its peak level and plateau at the 4th hour. The fT4 peak level increased 3.25 times compared to baseline. The shorter LT-4 absorption test with low doses may provide an alternative method to the commonly used longer protocols with higher doses to rule out malabsorption. Key Words: Levothyroxine absorption test, Pseudo-malabsorption, Resistant hypothyroidism.

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