Endocrine Abstracts

Background and objective: Increased prescription of levothyroxine (LT4) has been observed in the USA and countries in Europe and has been related to increased thyroid function screening and a lower treatment threshold, increasing risk for overdiagnosis and overtreatment. We wanted to study the evolution of LT4 prescriptions in Belgium, and compare the use of anti-arrhythmic drugs (AAD) and bone-anti-resorptive drugs (BAD) between LT4-users and non-LT4-users.

Method: Retrospective study, using reimbursement data from the largest health insurance company (Christelijke mutualiteit/Mutualité Chrétienne), representing 42% of all Belgian residents during years 2001 to 2018. Individuals with history of thyroid surgery or concurrent use of thiamazole drugs were excluded (2.1% of cohort). Data extracted: age, gender, socio-economic status (SES, defined by right for increased reimbursement), number of persons with at least one package of reimbursed LT4 that was delivered in the public pharmacy, dose, BAD, AAD.

Results: Whereas 2.1% of individuals were prescribed LT4 in year 2001, this rose to 5.1% in year 2018 (2.5-fold increase). The increase was most pronounced for individuals aged ≥65 and especially ≥80yo (11.2% in year 2018 vs 4.3% in year 2001). Furthermore in year 2018 and for the total cohort, the proportion of LT4-users was higher in females (8.2% vs 1.9% in males, year 2018) and higher in individuals with increased reimbursement (7.4% vs 4.7%, year 2018). In 10.9% only the lowest commercially available dose of LT4 (25 µg) was prescribed, with highest proportion (14.4%) in the ≥80yo subgroup. Finally, in individuals aged ≥65yo in year 2018 use of AAD was higher among LT4-users than non-LT4-users (58.6% vs 50.4%; OR=1.39; P < 0.00001). Also use of BAP was higher among LT4-users, especially in males (2.6% vs 1.9%; OR=1.3; P < 0.0001; females: 10.4% vs 9.8%; OR 1.03; P = 0.026).

Conclusions: In a large representative Belgian sample, we confirm increasing prescription of LT4, most pronounced in the elderly, raising concerns regarding potential overdiagnosis. The high proportion of lowest LT4 dose and higher concurrent use of anti-arrhythmic and bone-anti-resorptive drugs among older LT4-users could point to overtreatment, but warrants further study.