Background: The objective of this study was to define the incidence and prevalence of treated thyroid dysfunction in a complete and representative population base.
Method: We used record-linkage technology to retrospectively identify subjects treated for hyperthyroidism or hypothyroidism in the general population of Tayside, Scotland from 1 January 1993 to 30 April 1997. Thyroid status was ascertained by record-linkage of patient-level datasets containing details of treatments for hypothyroidism (thyroid replacement therapy) and hyperthyroidism (radioactive iodine, surgical ablation or antithyroid medication).
Results: The fixed population of Tayside for the study period was 369,885. We identified 2,530 subjects who had been treated for hyperthyroidism. Of these 620 were classified as incident cases of hyperthyroidism, an incidence rate of 0.77 /1000 per year (95% CI 0.70-0.84) in females and 0.14 /1000 per year (0.12-0.18) in males. We identified 11,745 subjects as being treated for hypothyroidism. Of these 3,486 were classified as incident cases of primary hypothyroidism, an incidence rate of 4.98 /1000 per year (95% CI 4.81-5.17) in females, and 0.88 /1000 per year (95% CI 0.80-0.96) in males. For both hyperthyroidism and hypothyroidism, the incidence increased with age and females were affected two to eight times as much as males across the age range. The mid-year point-prevalence of all-cause hypothyroidism rose from 2.2% in 1993, to 3.0% in 1996. A case record validation exercise in 450 subjects showed the record-linkage methodology to perform well with positive predictive values of 0.98 for treated hyperthyroidism and 0.96 for treated hypothyroidism.
Conclusion: The level of thyroid dysfunction in Tayside Scotland is higher than previously reported in the UK and increased between 1993 and 1996.
22 - 24 Mar 2004
British Endocrine Societies