(100) Prevalence and Determinants of Over- and Undertreatment of Thyroid Dysfunctions in The Rhineland Study

Publication Number: 1145

Background: Levothyroxine (LT4) use is very high in Germany, but data on treatment adequacy are scarce.

Objectives: To assess prevalence and determinants of untreated hypothyroidism in LT4 non-users, over- and undertreatment in LT4 users, and low-normal and high-normal thyroid-stimulating hormone (TSH) levels in controlled users.

Methods: Analyses were based on cross-sectional data from the first 3000 participants of the Rhineland Study, a population-based cohort in Bonn, Germany, including people aged ≥30 years. Medication data were collected interview-based. We assessed the prevalence and determinants of untreated hypothyroidism in LT4 non-users with binomial logistic models. We assessed treatment status in LT4 users by TSH levels (controlled 0.56-4.27 mU/l; overtreated < 0.56 mU/l; undertreated >4.27 mU/l) and quantified their determinants (e.g. demographics/ comorbidities) in multinomial logistic regression models (reference group: controlled). Subsequently, controlled individuals were grouped into tertiles (low-normal, normal, and high-normal TSH) and the same methods were applied to assess determinants.

Results: The analytical sample comprised 2938 individuals (mean age 55 years, standard deviation (SD) 14.4, range 30-95; 57% women), of whom 23% reported LT4 use. 78% were classified as controlled, 18% as over-, and 4% as undertreated. In non-users of LT4, the odds of hypothyroidism were lower in men (odds ratio (OR) 0.52 95% confidence interval (CI) 0.29-0.92) than in women and lower in those with self-reported depression (OR 0.19 95%CI 0.03-0.61) than in those without depression. Increasing BMI (OR 1.09 CI 95%CI 1.03-1.14) resulted in higher odds of hypothyroidism.
Among LT4 users, older age (OR 1.03 95% CI 1.01-1.08) was associated with higher odds of overtreatment. Higher LT4 dose was associated with higher odds of both over- (OR 1.02 95%CI 1.02-1.03) and undertreatment (OR 1.02 95%CI 1.00-1.03). Mean TSH in controlled users was 1.6 mU/l (SD 0.8). In controlled users, lower odds of low-normal TSH were observed in men (OR 0.51 95%CI 0.26-1.00) compared to women and iodine supplement users were more likely than non-users to have low-normal TSH (OR 1.80 95%CI 1.04-3.11).
Individuals in the low-normal (OR 0.52 95%CI 0.30-0.90) and high-normal (OR 0.48 95%CI 0.26-0.90) ranges were more likely to have poorer cognitive performance. With increasing age, the likelihood of having a high-normal TSH level decreased (OR 0.96 95%CI 0.93-0.99).

Conclusions: LT4 use is suboptimal in our population: 22% are inadequately treated, resulting in high absolute numbers. There seems to be a tendency to treat towards lower levels of TSH (overtreatment), which is noteworthy in that lower TSH levels, even in the normal range, are associated with negative health outcomes.