Laboratory Diagnosis of Thyroid and Adrenal Disease

Area of Science:

• Veterinary Medicine
• Endocrinology
• Canine Health

Background:

• Diagnosing canine thyroid and adrenal diseases presents challenges, particularly for hypothyroidism and naturally occurring Cushing's syndrome (NOCS).
• Hyperthyroidism and hypoadrenocorticism have more straightforward diagnostic criteria compared to hypothyroidism and NOCS.
• Misinterpretation of diagnostic results can lead to delayed or incorrect diagnoses in affected animals.

Purpose of the Study:

• To elucidate the diagnostic approaches for canine hypothyroidism and naturally occurring Cushing's syndrome.
• To provide guidance on the interpretation of diagnostic tests for these complex endocrinopathies.
• To assist veterinarians in making definitive diagnoses for thyroid and adrenal diseases in dogs.

Main Methods:

• Review of diagnostic criteria for hyperthyroidism and hypothyroidism.
• Analysis of the ACTH stimulation test (ACTHst) for hypoadrenocorticism and NOCS.
• Discussion of appropriate diagnostic pathways and result interpretation for canine endocrinopathies.

Main Results:

• A single elevated total thyroxine (tT4) level is sufficient for diagnosing hyperthyroidism.
• A low tT4 level alone is insufficient for diagnosing hypothyroidism.
• A flat ACTH stimulation test result (post-stimulation cortisol <2 ug/dL) confirms hypoadrenocorticism, but NOCS cases may not always show elevated ACTHst results.

Conclusions:

• Accurate diagnosis of hypothyroidism and NOCS requires careful consideration of clinical signs alongside specific diagnostic tests.
• Understanding the limitations and proper interpretation of tests like tT4 and ACTHst is crucial for veterinary endocrinology.
• This article serves as a guide for selecting and interpreting diagnostics for common canine thyroid and adrenal diseases.