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Dr. Kumar Prafull Chandra, Director, Dept. of Internal Medicine & Diabetes care, Healthcity Vistaar Hospital; and, Chandra Diabetes & Obesity Clinic, Gomtinagar, Lucknow 07 April 2024
Thyroid function test (TFT) interpretation is generally straightforward. However, certain conditions can lead to unusual TFT patterns that require careful clinical correlation.
The hypothalamus releases thyrotropin-releasing hormone, which stimulates the pituitary gland to release thyroid-stimulating hormone (TSH). TSH then prompts the thyroid gland to release thyroid hormone (T4 and T3), which provides negative feedback to the pituitary gland to regulate TSH secretion. This creates a tightly controlled equilibrium in thyroid hormone release. Even small changes in free-T4 levels can result in significant alterations in TSH, making it a sensitive parameter for assessing thyroid function.
However, in certain conditions, the feedback mechanism malfunctions, such as – central hypothyroidism, non-thyroidal illness, recently treated thyrotoxicosis, resistance to thyroid hormone, TSH secreting pituitary adenoma.
Diagnosis of thyroid dysfunction must follow:
Clinical Conditions:
Euthyroid sick syndrome: Common finding after chronic illness. Pre-illness TFT is detrimental in assessing thyroid hormone replacement therapy.
Heterophilic Antibody Interference: Incidence 0.05%-6%. Heterophilic antibodies like Human Anti-Mouse (HAMA) can cause falsely elevated TSH levels.
Conditions leading to Thyroid Hormone Resistance:
Discordant TFTs – Steps to follow when Thyroid function fails to respond to the clinical scenario:
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