Thyroid testing for genetic screening purposes is less likely to be meaningful before puberty. Screening is initiated, therefore, once healthy dogs and bitches have reached sexual maturity (between 10-14 months in males and during the first anestrous period for females following their maiden heat). As the female sexual cycle is quiescent during anestrus, any influence of sex hormones on baseline thyroid function will be minimized. This period generally begins 12 weeks from the onset of the previous heat and lasts one month or longer. The interpretation of results from baseline thyroid profiles in intact females will he more reliable when they are tested in anestrus. Once the initial thyroid profile is obtained, dogs and bitches should be rechecked on an annual basis to assess their thyroid function and overall health. Obtaining annual test results provides comparisons that permit early recognition of developing thyroid dysfunction. This allows for prompt treatment, where indicated, to avoid the appearance or advancement of clinical signs associated with hypothyroidism.

Screening for Canine Autoimmune Thyroiditis

•  Complete thyroid antibody profile required
•  Test intact bitches during anestrus
•  Need T3AA, T4AA, TgAA; not just freeT4, TSH, TgAA
•  OFA Thyroid Registry is a limited panel
•  Some cases (~8%) are T3AA and/or T4AA +, but TgAA -

Treating Canine Autoimmune Thyroiditis

•  Treat cases + for T3AA and/or T4AA, or TgAA with thyroxine
•  While controversial, clinical evidence supports this approach rather than  waiting until dog gets ill or has aberrant behavior†
•  If only low-grade TgAA + , retest profile in 2-4 mos
•  Treat with thyroxine BID; retest profile in 2-4 mos
•  Always monitor with thyroid antibody profile
•  For recently vaccinates, wait 90 days before retesting

Do not breed dogs with autoimmune thyroiditis

•  Heritable trait, regardless of clinical status
•  Screen relatives annually from puberty
•  Consider for breeding, if negative, after age three

†Data from humans and dogs with thyroiditis show that AA levels gradually become reduced over a period of 5-10 months. This is believed to result from negative feedback inhibition of pituitary TSH production, which in turn, reduces stimulation of receptors mediating the targeted lymphocytic destruction of thyroid acinar cells.

[To be continued next month, with discussion of diagnostic profile recommendations and interpretations]

References: Nachreiner RE, Refsal KR, JAVMA 201: 623-629, 1992; Thacker EL et al, AJVR 53: 449-453, 1992; Nachreiner RE et al, AJVR 54: 2091-2098, 1993; Dewey CW et al, Prog Vet Neurol 6: 117-123, 1995; Dodds WJ, Adv Vet Sci Comp Med, 39: 29-96, 1995; Thacker EL et al, AJVR 56: 34-3 8, 1995; Peterson ME et al, JAVMA 211:1396-1402, 1997; Dodds WJ, Can Pract 22 (1): 18-19, 1997; Nachreiner RE et al, AJVR 59:951-955, 1998; Scott-Moncrieff JCR et al, JAVMA 212:387-391, 1998; Scott-Moncrieff JCR, Nelson RW, JAVMA 213:1435-1438, 1998; Iverson L et al, Vet Clin Pathol 28:16-19, 1999; Jensen AL et al, J Comp Pathol 114: 339-346, 1999; Dodds WJ, Aronson LP, Proc AHVMA, 80-82, 1999; Scott-Moncrieff JC et al, JAVMA 221: 515-521, 2002; Beaver BV, Haug LI, JAAHA 39: 43 1-434, 2003.