The OFA Thyroid Registry Profile is offered by Antech Diagnostics (New York branch), and the required OFA forms and instructions for testing must be used. The profile includes: freeT4 ED, cTSH, and TgAA. This profile may fail to identify up to 8% of dogs with autoimmune thyroid disease that are T3AA and/or T4AA positive but TgAA negative.

Accordingly, to avoid missing this subset of cases, a preferred approach is to measure the complete thyroid antibody profile which includes the OFA Registry Profile plus T4, T3, freeT3, T3AA, and T4AA. This approach is especially important for evaluating breeding stock and family background.

Follow up testing is beneficial to ensure adequacy of the prescribed dosage as well as client compliance. For dogs receiving thyroid supplementation, measuring the total T4 and free T4 is recommended at the peak sampling time of 4-6 hours post-BID therapy. [Alternatively, a trough level or both peak and trough levels also can be run.] Both tests are needed because measuring T4 alone could lead to an inappropriate dose increase if a sub-optimal T4 result is due to concomitant NTI or use of certain drugs listed above. For dogs with thyroiditis, however, post-thyroxine monitoring should include the complete thyroid antibody profile to determine whether thyroid autoantibodies are waning as anticipated.

Monitoring patients on thyroxine is recommended at least once a year and ideally twice a year. The pharmacokinetics, metabolism and excretion of the drug can vary from individual-to-individual or over time in the same individual, resulting in an absorption rate that ranges from 12-55% (mean 37%). Further, on the day of testing, the medication should be given directly by mouth and not with a meal, as calcium binds to thyroxine and can retard absorption of the drug.

Please note that the reported reference ranges for these tests reflect basal and not peak therapeutic levels, and that peak levels for dogs receiving levothyroxine should be in the upper 1/3 to 1/3 above the upper limits of the basal ranges for good metabolic control.

Please ask about Antech's new thyroid profiles:
86100: OFA, FT4(ED), TGAA, TSH, T3, T4, FreeT3, FreeT4, T3AA, T4AA
86101: OFA,FT4(ED), TGAA, TSH, T3AA, T4AA

References: Peterson et al, JAVMA 211: 1396-1402, 1997; Dodds, Scott-Moncrieff et al, JAVMA 212: 387-391, 1998; Wolfsheimer, Adv Sm An Med Surg 11(7): 1-3, 1998; Nachreiner et al, AJVR 59: 951-955, 1998; Antech News, November 1998; Bruner et al, JAVMA 212: 1572-1575, 1998; Dodds, Proc AHVMA, pp. 77-79 and 80-82, 1999; Iverson L et al, Vet Clin Pathol 28:16-19, 1999; Jensen AL et al, J Comp Pathol 114: 339-346, 1999; Nachreiner, RF et al. JAVMA 220:466 - 471, 2002; Scott-Moncrieff, JC et al. JAVMA 221:515-521, 2002.