An estimated 80% of cases of canine hypothyroidism result from heritable autoimmune (lymphocytic) thyroiditis. The top ten dog breeds diagnosed with autoimmune thyroiditis include: Golden retriever, Shetland sheepdog, American cocker spaniel, Labrador retriever, Boxer, Doberman pinscher, German shepherd, Akita, Old English sheepdog, and Irish setter, although many more breeds are also affected.

The presence of elevated TgAA levels confirms thyroiditis, promotes early recognition of the disorder, and facilitates genetic counseling. The currently available commercial assay for canine TgAA uses an ELISA method. False positive results can occur if the dog has been vaccinated recently. Dogs on thyroid supplement should be off this medication for at least 90 days to obtain accurate TgAA results.

Whereas essentially all cases of autoimmune thyroiditis should have elevated TgAA in their serum, only about 20% have elevated serum T3 and/or T4 AA. Thus, the presence of elevated T3 and/or T4 AA confirms a diagnosis of autoimmune thyroiditis but underestimates its prevalence, as negative (non-elevated) serum T3 and/or T4 AA levels do not rule out thyroiditis. Most circulating antibodies are against T3 (~ 70%), some affect both T3 and T4 (~ 25%), and only a few affect T4 alone (~ 5%). When these antibodies are present, measurement of T4 and T3 levels will be spuriously high.

The K value was introduced 10 years ago to express the relationship between serum free T4 and cholesterol levels, as a means of assessing thyroid function. Since then, other thyroid tests and improved methods have become available that make it obsolete. As of November 1st, Antech Diagnostics will no longer report out the K value. If your clinic still wishes to receive this calculation, please call Customer Service.

For dogs receiving thyroid supplementation, we recommend measuring at least the total and free T4 at the peak sampling time of 4-6 hours post-BID therapy. Both peak and trough levels can also be run. Please note that the reported reference ranges for these tests reflects basal and not peak therapeutic levels, which should be in the upper third to 25% above the upper limits of the basal ranges for good control.

A complete range of thyroid function tests is offered by Antech Diagnostics either as a series of different thyroid profiles or as part of a comprehensive total health screening panel.

References: Panciera, Vet Med 92: 44-68, 1997; Peterson et al, JAVMA 211: 1396-1402, 1997; Dodds, Can Pract 22(1): 18-19, 1997; ibid, Adv Vet Sci Comp Med 39: 29-96, 1995; ibid, Proc AHVMA 82-95, 1997; Scott-Moncrieff et al, JAVMA 212: 387-391, 1998; Wolfsheimer, Adv Sm An Med Surg 11(7): 1-3, 1998.