In thyrotoxicosis, what is the typical pattern of TSH and thyroid hormone levels?

In thyrotoxicosis, what is the typical pattern of TSH and thyroid hormone levels?

• A. Decreased TSH with increased T3/T4
• B. Normal TSH with normal T3/T4
• C. Increased TSH with increased T3/T4
• D. Increased T3 and T4 with decreased TSH

Answer: (D)

Thyrotoxicosis raises circulating thyroid hormones, and the pituitary responds with suppressed TSH due to negative feedback. The typical lab pattern is elevated free T3 and/or T4 with a decreased TSH. This reflects primary overproduction of thyroid hormone (often with T3-predominant thyrotoxicosis in some cases, yet TSH remains suppressed). If TSH were elevated with high thyroid hormones, that would point to a TSH-secreting pituitary problem rather than classic thyrotoxicosis. Normal TSH with normal thyroid hormones would be euthyroid, and low hormones with low TSH would not represent thyrotoxicosis.

Thyrotoxicosis raises circulating thyroid hormones, and the pituitary responds with suppressed TSH due to negative feedback. The typical lab pattern is elevated free T3 and/or T4 with a decreased TSH. This reflects primary overproduction of thyroid hormone (often with T3-predominant thyrotoxicosis in some cases, yet TSH remains suppressed). If TSH were elevated with high thyroid hormones, that would point to a TSH-secreting pituitary problem rather than classic thyrotoxicosis. Normal TSH with normal thyroid hormones would be euthyroid, and low hormones with low TSH would not represent thyrotoxicosis.