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When a dog suspected to have hypothyroidism has a low total T4 concentration, fT4 and/or TSH concentrations must be evaluated to help confirm or refute the diagnosis (TABLE 1). If the TSH concentration is high, hypothyroidism can be diagnosed.
• Dogs with T4 results in the low normal range may be hypothyroid. In dogs with low or low normal T4 results and with consistent clinical signs, consider one or more of the following to aid in confirming hypothyroidism: • Free T4 (fT4) • Endogenous thyroid-stimulating hormone (TSH) • Possible thyroglobulin autoantibodies (TgAA)
Total T4 (TT4) Canine Evaluation of total T4 (TT4) is best used to rule out a diagnosis of hypothyroidism or monitor dogs on levothyroxine supplementation. TT4 concentrations below the lower reference limit are suspicious (but not confirmatory) for hypothyroidism. Evaluation of FT4 and TSH is recommended, if hypothyroidism is clinically suspected.
TSH is normal in many abnormal dogs, so we recommend measuring it in combination with other thyroid function tests. Thyroglobulin autoantibody (TgA) testing is recommended for dogs with a breed predilection for autoantibody problems or those with unexpectedly high T3 or T4 values.
1 lut 2004 · One of the most common situations is the observation of a normal TSH in face of low total T4 or free T4 by equilibrium dialysis. It should be recognized that a significant proportion (15-25 percent) of hypothyroid dogs may have a normal TSH.
Abnormally high concentrations of T4, as seen in hyperthyroidism (a very rare condition in the dog) will inhibit TSH secretion and cause low serum concentrations of TSH. Unfortunately, current assays for canine TSH do not have sufficient sensitivity to differentiate normal from low concentrations.
18 paź 2021 · Because as many as one-third of hypothyroid dogs will have a TSH level within the reference interval, a normal TSH result cannot be used to rule out hypothyroidism. In these cases, a clinical presentation suspicious for hypothyroidism, exclusion of nonthyroidal factors, a low TT4 and fT4 result, and a TSH level in the middle to upper end of the ...
