Serum iodine concentrations in euthyroid dogs and dogs with autoimmune thyroiditis and hypothyroidism.

Serum iodine concentration is not a reliable diagnostic marker for autoimmune thyroiditis or hypothyroidism in dogs.

This retrospective observational study characterized total and inorganic serum iodine concentrations in dogs with varying thyroid disease status, using leftover serum samples submitted to the Michigan State University Veterinary Diagnostic Laboratory between January and June 2023. Three groups were evaluated: euthyroid dogs (n = 86), dogs with autoimmune thyroiditis confirmed via thyroglobulin autoantibody (n = 101), and dogs with hypothyroidism (n = 97). Iodine concentrations were measured using inductively coupled plasma-mass spectrometry, and a reference interval was established from the euthyroid population. Results demonstrated that serum iodine concentrations varied widely across all groups, but elevated iodine levels were not associated with either autoimmune thyroiditis or hypothyroidism when compared to euthyroid controls. Notably, statistically significant differences in both total and inorganic iodine concentrations were identified between dogs with autoimmune thyroiditis and those with hypothyroidism, suggesting these two conditions may differ in iodine dynamics. However, the clinical significance of this difference remains unclear. The authors conclude that serum iodine concentration alone is not a reliable biomarker for thyroid disease in dogs and should not be used diagnostically to identify autoimmune thyroiditis or hypothyroidism. These findings are relevant for clinicians considering iodine status as a contributing factor to canine thyroid disease and reinforce that standard thyroid screening panels remain the appropriate diagnostic approach.

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