Subclinical hyperthyroidism is best described by which pattern of TSH and FT4/TT3/TT4?

• A. TSH low; FT4 normal; TT3/TT4 normal
• B. TSH high; FT4 normal; TT3/TT4 normal
• C. TSH normal; FT4 high; TT3/TT4 high
• D. TSH normal; FT4 normal; TT3/TT4 normal

Answer: (A)

Subclinical hyperthyroidism shows a suppressed TSH with normal thyroid hormone levels. The pituitary reduces TSH production in response to a slight excess of thyroid activity, but free T4 and T3 remain within their normal ranges. So the best description is low TSH with normal FT4 and TT3/TT4. The other patterns don’t fit: high TSH with normal hormones points to subclinical hypothyroidism; normal TSH with high hormones suggests overt hyperthyroidism; and normal TSH with normal hormones means euthyroid.