Characterization of thyroid function and antithyroid antibody tests among Saudis

Objective: To determine the reference intervals for thyroid function tests and the prevalence of thyroid autoimmunity in the Saudi population. Methods: A cross-sectional prospective study was conducted in King Khalid University Hospital, Riyadh, Saudi Arabia from January to June 2013. History and physical examination were obtained. Thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) were measured by Electro-chemiluminescence Immunoassay system-assay. Antithyroperoxidase, and anti-thyroglobulin antibodies were measured using enzyme-linked immunosorbent-assay. Subjects with previous or a family history of thyroid disorders, those taking medications affecting thyroid function, pregnant or lactating women, and those with goiter were excluded. Individuals with positive antibodies were excluded from the final analysis of the TSH reference range, but were used to determine the prevalence of thyroid autoimmunity. Results: Out of 337 Saudi subjects initially screened, 132 (aged 13-60 years) were candidates for reference calculation, the mean +/- standard deviation, and (2.5th-97.5th) percentile of TSH (mIU/L) was 1.96 +/- 0.9 (0.59-4.37), for FT4 (pmol/L) was 15.47 +/- 1.83 (12.04-19.13), and for FT3 (pmol/L) was 5.22 +/- 0.7 (4.07-6.76). The TSH was higher in the antibodies positive group (2.5 +/- 1.17 mIU/L) compared with the negative one (1.96 +/- 0.9 mIU/L) (p<0.05). Finally, 26% of subjects were tested positive for antithyroid antibodies. Conclusion: The TSH reference range was similar to laboratory references. Thyroid antibodies were prevalent in Saudis, necessitating further work in larger scale studies.