This article presents a complex clinical case of a 26-year-old female patient with autoimmune polyglandular syndrome type 2, comprising type 1 diabetes mellitus, primary adrenal insufficiency, and autoimmune thyroiditis with severe decompensated hypothyroidism (thyroid stimulating hormone 491.84 mU/L) despite treatment with high doses of levothyroxine sodium (L-T4) – 350 mcg/day.

    The key diagnostic challenge was to differentiate true L-T4 malabsorption from pseudomalabsorption caused by polypharmacy, non-adherence to the medication regimen, and psychosomatic disorders.

   To verify the cause, an L-T4 absorption test was performed using a 600 mcg dose of L-T4, with monitoring of free thyroxine (fT4) levels. The test results demonstrated an adequate increase in fT4 of more than 240% over 6 hours, which allowed for the exclusion of true malabsorption. Based on these findings, a comprehensive therapy correction was implemented: the sequence of drug administration was optimized (L-T4 to be taken strictly on an empty stomach with a subsequent interval before taking other medications), the glucocorticoid dose was reduced, insulin therapy was adjusted, and psychotherapeutic support was prescribed. This case highlights the critical importance of objectively assessing L-T4 absorption in patients with polyendocrinopathies to select the optimal pathway for achieving hypothyroidism compensation and to develop a personalized management plan.