Objective:

To determine the incidence and prevalence of hypothyroidism, stratifying by sex and age, as well as the cost per defined daily dose (cDDD) of levothyroxine.

Design:

Observational, descriptive, longitudinal, retrospective study.

Setting:

Aljarafe-Sevilla Norte Health Area.

Participants:

Patients of any age and either sex living in this Health Area, who were treated with levothyroxine in 2015-2017 and who had at least two consecutive blood tests for thyroid control between 2014-2017

Main measures:

Levels of thyrotropin, thyroxine, and anti-thyroid peroxidase antibodies were determined, provided by the Laboratory Unit of the Hospital San Juan de Dios. Data on levothyroxine prescription and its cost per defined daily dose were also determined, provided by the Pharmacy Unit of the Distrito Sanitario Sevilla-Norte. We considered the cost of the mean value per defined daily dose of levothyroxine.

Results:

45,224 thyroid tests were analysed. 78.4% belonged to women. The average age was 49.04 (SD: 21.24). The prevalence (2017) of hypothyroidism was 5.54% (95% CI: 5.45-5.62), the cumulative incidence of clinical hypothyroidism was 2.67 cases/1000 persons-year (95% CI: 2.67-2.68) and of subclinical hypothyroidism was 52.04 cases/1000 persons-year (95% CI: 52.01-52.06). The annual average cost associated with levothyroxine use was 153,081.13 € (SD: 12,662.03) (95% CI: 152,964.43-153,197.83).

Conclusions:

This study establishes the first data on cumulative incidence of hypothyroidism in a Spanish area and presents a higher prevalence compared to most of the previous studies. Likewise, it shows a cost per defined daily dose (cDDD) of levothyroxine which followed an upward trend in the period 2015-2017.

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