A 17-year-old adolescent comes to the clinic because of weight loss, irritability, insatiable hunger, and heat intolerance. The PNP screens for hyperthyroidism. In the patient with hyperthyroidism:

A 17-year-old adolescent comes to the clinic because of weight loss, irritability, insatiable hunger, and heat intolerance. The PNP screens for hyperthyroidism. In the patient with hyperthyroidism:

• A. The TSH level is normal, and the T4 level is elevated.
• B. The TSH and the T4 levels are elevated.
• C. The TSH level is normal, and the T4 level is below normal.
• D. The TSH level is below normal, and the T4 level is elevated.

Answer: (D)

Excess thyroid hormone suppresses the pituitary’s output of TSH through negative feedback, so in hyperthyroidism the expected lab pattern is a low TSH with an elevated T4 (often with higher T3 as well). In this adolescent, weight loss, irritability, increased hunger, and heat intolerance point to hyperthyroidism, so the pituitary responds by lowering TSH while the thyroid produces more T4. The combination described fits primary hyperthyroidism: low TSH and high T4. The other patterns don’t match this mechanism—for example, normal TSH with high T4 would not reflect pituitary suppression, both hormones elevated suggests a different or secondary cause, and normal TSH with low T4 points to hypothyroidism.

Excess thyroid hormone suppresses the pituitary’s output of TSH through negative feedback, so in hyperthyroidism the expected lab pattern is a low TSH with an elevated T4 (often with higher T3 as well). In this adolescent, weight loss, irritability, increased hunger, and heat intolerance point to hyperthyroidism, so the pituitary responds by lowering TSH while the thyroid produces more T4. The combination described fits primary hyperthyroidism: low TSH and high T4. The other patterns don’t match this mechanism—for example, normal TSH with high T4 would not reflect pituitary suppression, both hormones elevated suggests a different or secondary cause, and normal TSH with low T4 points to hypothyroidism.