Celiac disease is more common in patients with hypothyroidism. Malabsorption of levothyroxine has not been studied in this population. We sought to determine if levothyroxine dosing was influenced by the presence and treatment of celiac disease.

This retrospective study was conducted at an academic medical center. Cases had hypothyroidism and celiac disease. Controls had hypothyroidism alone and were selected randomly through the endocrinology clinic records. Celiac disease was defined as representative pathology with positive serology. Age, sex, height, weight, body mass index, creatinine, and medical comorbidity were assessed for cases and controls. The levothyroxine dose and weight-based levothyroxine dose necessary to maintain a euthyroid state was evaluated for controls, and before and after celiac disease therapy for cases.

Celiac disease was identified in 152 patients, and 22 patients had concomitant hypothyroidism (14.5%). Seven cases met inclusion criteria. Overall, 200 control patients were identified. The mean celiac disease pretreatment levothyroxine dose and weight-based levothyroxine dose needed to maintain a euthyroid state were higher in cases than in controls (154 μg vs 106 μg, P=.007, and 2.6 μg/kg vs 1.3 μg/kg, P <.001). Doses decreased significantly after treatment of celiac disease (154 μg vs 111 μg, P=.03; and 2.64 μg/kg vs 1.89 μg/kg, P=.04). All cases required at least 125 μg of levothyroxine initially to maintain a euthyroid state.

Levothyroxine malabsorption likely occurs with hypothyroidism and untreated celiac disease. Absorption may improve after celiac disease treatment. Screening for celiac disease in patients with hypothyroidism requiring elevated levothyroxine doses warrants further investigation.