A patient presents with elevated TSH levels despite normal T4 levels. Which mechanism explains why negative feedback regulation is ineffective in suppressing TSH secretion in this specific condition?

💡 Explanation

Impaired T4 to T3 conversion causes ineffective negative feedback because T3, rather than T4, is the primary active thyroid hormone that inhibits TSH release from the pituitary gland. Therefore, TSH remains elevated despite normal T4 levels, rather than decreased iodine transport or receptor sensitivity being the cause.

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