Which laboratory result would indicate hyperthyroidism?

Which laboratory result would indicate hyperthyroidism?

• A. High TSH, low FT4 and FT3
• B. Normal TSH, FT4/FT3 normal
• C. High FT4 with FT3 and high TSH
• D. Low TSH, raised FT4 and FT3

Answer: (D)

In hyperthyroidism the thyroid gland overproduces hormones, so the circulating levels of free T4 and free T3 rise. The higher thyroid hormone levels feed back to the pituitary, reducing TSH secretion. So the classic lab picture for primary hyperthyroidism is low or suppressed TSH with elevated free T4 and free T3. This combination reflects the thyroid dominance over the axis and the pituitary’s attempt to compensate by dialing TSH down. Other patterns don’t fit hyperthyroidism well. A high TSH with low FT4/FT3 points to hypothyroidism or thyroid failure rather than overactivity. Normal TSH with normal FT4 and FT3 suggests a euthyroid state. High FT4 with FT3 and high TSH could indicate a central (pituitary) cause of thyrotoxicosis, not the typical primary hyperthyroid picture. The key clue for hyperthyroidism is the low TSH alongside raised free thyroid hormones.

In hyperthyroidism the thyroid gland overproduces hormones, so the circulating levels of free T4 and free T3 rise. The higher thyroid hormone levels feed back to the pituitary, reducing TSH secretion. So the classic lab picture for primary hyperthyroidism is low or suppressed TSH with elevated free T4 and free T3. This combination reflects the thyroid dominance over the axis and the pituitary’s attempt to compensate by dialing TSH down.

Other patterns don’t fit hyperthyroidism well. A high TSH with low FT4/FT3 points to hypothyroidism or thyroid failure rather than overactivity. Normal TSH with normal FT4 and FT3 suggests a euthyroid state. High FT4 with FT3 and high TSH could indicate a central (pituitary) cause of thyrotoxicosis, not the typical primary hyperthyroid picture. The key clue for hyperthyroidism is the low TSH alongside raised free thyroid hormones.