Diagnosis

Diagnosis of hypothyroidism can be challenging. There is no single test that is completely accurate in identifying the truly hypothyroid dog.

For a definitive diagnosis of hypothyroidism, minimizing false positives and negatives requires evaluation of a variety of parameters.

Click the thumbnail to for a diagnosis table.

Most hypothyroid dogs are middle aged and medium to large breeds.

Source: Dr. Carmel Mooney

Hypothyroidism affects multiple organ systems, a complete laboratory workup is warranted including complete blood count (CBC), biochemistry screen and urinalysis.

Characteristic findings are normocytic, normochromic, non-regenerative anemia and hypercholesterolemia.

In dogs with no evidence of non-thyroidal disease

• tT4 within the reference range rules out hypothyroidism in most cases
• tT4 below the reference range means that further thyroid testing is necessary to confirm the diagnosis

tT4 below reference range may be due to:

• Concurrent disease (euthyroid sick syndrome)
• Long-term drug therapy with highly protein-bound compounds that compete for tT4 binding sites.

Not all laboratories use the same units of measure and of course one laboratory's reference range for acceptable values will differ from another. The two units of measure used for measuring tT4 are µg/dl and nmol/l. To convert from nmol/l to µg/dl use the following equation: nmol T4 /l x 0.0777 = µg T4 /dl.