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

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

Answer: (A)

Subclinical hypothyroidism occurs when the pituitary detects a slight drop in thyroid hormone activity and increases TSH, but the circulating thyroid hormones themselves stay within the normal range. That’s why the pattern is an elevated TSH with normal free T4 (and normal T3/T4, whether free or total). In this stage, patients often have no overt symptoms or only mild ones, and thyroid hormone levels have not fallen below the reference range yet. This distinguishes it from overt hypothyroidism, where free T4 would be low, and from hyperthyroidism, where TSH would be suppressed.