TSH Canine
Description
Production and Physical Properties
TSH Canine is produced via recombinant DNA technology in mammalian cell lines, co-expressing both subunits . Key physical properties include:
Biological Role and Diagnostic Applications
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Euthyroid sick syndrome: Non-thyroidal illnesses may suppress T4/fT4 without elevating TSH
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TSH isoforms: Current assays detect only one isoform, missing 25–40% of hypothyroid cases
TRH Stimulation Test
| Parameter | Healthy Dogs | Hypothyroid Dogs | Euthyroid Sick Dogs |
|---|---|---|---|
| Baseline TSH (ng/mL) | 0.25 | 0.93 | 0.21 |
| TSH % Change (post-TRH) | 207% | 24% | 167% |
| Data from |
This test differentiates hypothyroidism from euthyroid sick syndrome with 90% accuracy but offers limited advantage over baseline TSH/T4 measurements .
Recombinant Human TSH Stimulation
A 75 μg/dog IV dose of recombinant human TSH achieves high diagnostic accuracy:
| Post-TSH T4 (μg/dL) | Classification | Sensitivity/Specificity |
|---|---|---|
| <1.3 | Hypothyroid | 92.5%/97.3% |
| >1.7 | Euthyroid | 100%/93.2% |
| Data from |
Breed-Specific Variations and Reference Ranges
Significant breed-associated differences in thyroid function exist:
A 2024 study reported median TSH levels of 0.2 ng/mL (range: <0.03–2.6 ng/mL) in dogs, with 26% exceeding reference ranges .
Limitations of Current Diagnostics
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TSH Assay Sensitivity: Detects only one isoform, missing hypothyroid cases with normal TSH
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Non-Thyroidal Illness: Low T4 without TSH elevation complicates diagnosis
Emerging Methods
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TRH Stimulation + GH Measurement: Basal growth hormone (GH) levels >3.5 ng/mL suggest hypothyroidism in dogs with low T4/normal TSH
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Thyroid Uptake Scintigraphy: Technetium-99m imaging provides definitive thyroid reserve assessment
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Therapeutic Trials: Levothyroxine response remains the gold standard for confirmation
Research and Clinical Implications
TSH Canine’s recombinant form enables precise calibration in immunoassays but lacks confirmed biological activity . Studies emphasize the need for:
Product Specs
Mammalian cell line.
Q&A
Experimental Design for TSH Assays in Canine Research
Question: What experimental design considerations should be taken into account when evaluating the sensitivity and specificity of TSH assays in canine research? Answer:
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Assay Selection: Choose assays with high precision and sensitivity, such as chemiluminescent immunometric assays, which have shown better performance in canine TSH measurement .
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Sample Size and Population: Ensure a diverse sample size that includes both healthy dogs and those with thyroid disorders to accurately assess assay performance.
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Data Analysis: Use statistical methods to evaluate within-run and between-run variability to ensure assay reliability.
Interpretation of TSH Results in Canine Hypothyroidism
Question: How should TSH results be interpreted in the context of canine hypothyroidism, especially when considering non-thyroidal illness? Answer:
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Combination with Other Tests: Interpret TSH results alongside total T4 levels and clinical signs. High TSH with low T4 is indicative of hypothyroidism, but normal or low TSH does not rule it out .
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Non-Thyroidal Illness (NTI): Consider NTI, which can affect T4 levels without altering TSH significantly. Additional tests like free T4 may help differentiate true hypothyroidism from NTI effects .
Contradictions in TSH and T4 Results
Question: What are the common contradictions observed between TSH and T4 results in canine thyroid function tests, and how can they be resolved? Answer:
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False Negatives and Positives: Up to 24% of hypothyroid dogs may not show elevated TSH, and up to 18% of normal dogs may have elevated TSH .
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Resolution Strategies: Use additional tests like the TRH stimulation test or measure growth hormone levels to confirm hypothyroidism in cases of discordant results .
Role of Growth Hormone in Canine Thyroid Regulation
Question: How does growth hormone influence thyroid hormone regulation in dogs, and what implications does this have for TSH testing? Answer:
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Growth Hormone Influence: Approximately 30% of thyroid hormone regulation in dogs is influenced by growth hormone, which can lead to false negatives or positives in TSH tests .
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Diagnostic Considerations: Consider measuring basal growth hormone levels or using a TRH stimulation test to improve diagnostic accuracy in cases where TSH results are inconclusive .
Advanced Diagnostic Techniques for Canine Hypothyroidism
Question: What advanced diagnostic techniques can be employed to improve the accuracy of canine hypothyroidism diagnosis beyond traditional TSH and T4 tests? Answer:
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TRH Stimulation Test: This test can help differentiate between true hypothyroidism and non-thyroidal illness by measuring TSH and growth hormone responses to TRH .
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Recombinant Human TSH Stimulation Test: This method is highly reliable for distinguishing between hypothyroid and euthyroid dogs, even in complex cases .
Statistical Analysis of TSH Data
Question: What statistical methods are appropriate for analyzing TSH data in canine research, particularly when comparing different assay methods? Answer:
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Precision and Correlation Analysis: Evaluate within-run and between-run precision using coefficients of variation (CV). Correlate results from different assays to assess agreement and reliability .
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Receiver Operating Characteristic (ROC) Curve Analysis: Use ROC curves to determine the sensitivity and specificity of TSH assays in diagnosing hypothyroidism .
Impact of Non-Thyroidal Illness on TSH Interpretation
Question: How does non-thyroidal illness affect TSH levels and interpretation in canine thyroid function tests? Answer:
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Effect on T4 Levels: Non-thyroidal illness can decrease T4 levels without affecting TSH, leading to false positives for hypothyroidism .
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Diagnostic Approach: Use a combination of TSH, total T4, and free T4 tests to differentiate true hypothyroidism from effects of non-thyroidal illness .
Comparison of TSH Assay Methods
Question: What are the advantages and limitations of different TSH assay methods (e.g., immunoradiometric, enzyme immunometric, chemiluminescent) in canine research? Answer:
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Chemiluminescent Assays: Offer better precision and sensitivity compared to other methods, making them preferable for canine TSH measurement .
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Limitations: Current assays may not accurately differentiate between normal and low TSH levels, limiting their use in diagnosing hyperthyroidism .
TSH in Canine Autoimmune Thyroiditis
Question: How does TSH relate to autoimmune thyroiditis in dogs, and what additional tests are recommended for diagnosis? Answer:
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TSH Levels: Elevated TSH may be seen in autoimmune thyroiditis due to thyroid gland destruction.
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Additional Tests: Thyroglobulin autoantibody (TgAA) testing is recommended to confirm autoimmune thyroiditis .
Future Directions in Canine TSH Research
Question: What future research directions are promising for improving the diagnosis and understanding of thyroid disorders in dogs using TSH? Answer:
Product Science Overview
TSH is produced by the pituitary gland, a small gland located at the base of the brain. The secretion of TSH is regulated by the hypothalamus through the release of thyrotropin-releasing hormone (TRH). When TRH stimulates the pituitary gland, it releases TSH into the bloodstream. TSH then acts on the thyroid gland, prompting it to produce and release thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3) .
These thyroid hormones are crucial for various physiological processes, including metabolism, growth, and development. They influence the function of many organs and systems within the body, making the regulation of TSH and thyroid hormones vital for maintaining homeostasis.
Hypothyroidism is one of the most common endocrine disorders in dogs. It occurs when the thyroid gland fails to produce adequate amounts of T4 and T3. This condition can be classified into primary, secondary, and tertiary hypothyroidism, with primary hypothyroidism being the most prevalent in canines .
- Primary Hypothyroidism: This form results from the direct dysfunction of the thyroid gland. It is often caused by idiopathic thyroid gland atrophy or immune-mediated lymphocytic thyroiditis. In lymphocytic thyroiditis, the thyroid gland is progressively destroyed by the immune system, leading to a deficiency in thyroid hormone production .
- Secondary Hypothyroidism: This rare form is due to a deficiency in TSH production by the pituitary gland. It can result from pituitary malformations or neoplasia .
- Tertiary Hypothyroidism: This form, which has not been described in dogs, would result from a deficiency in TRH production by the hypothalamus .
The clinical signs of hypothyroidism in dogs are varied and can affect multiple systems due to the widespread influence of thyroid hormones. Common signs include lethargy, weight gain, cold intolerance, and dermatologic changes such as hair loss, dry skin, and recurrent infections . Less common signs can include neurological and cardiovascular abnormalities .
Diagnosing hypothyroidism involves a combination of clinical signs, laboratory tests, and hormone assays. Measuring serum T4 and TSH levels is crucial, but the diagnosis should not rely solely on low T4 concentrations. A comprehensive evaluation, including TSH stimulation tests, is often necessary to confirm the diagnosis .
The primary treatment for hypothyroidism in dogs is hormone replacement therapy with synthetic levothyroxine (T4). This therapy aims to restore normal thyroid hormone levels and alleviate clinical signs. Regular monitoring of thyroid hormone levels and adjusting the dosage as needed is essential for effective management .
