Assessment of thyroid function

M I Surks
Ophthalmology 1981, 88 (6): 476-8
The thyroid hormones Thyroxine (T4) and Triiodothyronine (T3) can be measured directly in serum by radioimmunoassay. Most serum T4 and T3 circulates bound to specific serum-binding proteins but the small unbound fraction, free T4, correlates best with hormonal activity. The free T4 concentration can be measured directly and also can be estimated from the T3-resin uptake as the free T4 index (FT4-I). In hypothyroidism, T4 and FT4-I are decreased and when the disorder results from thyroid gland failure, serum TSH will be elevated as well. Indeed, an increase in serum TSH is the most sensitive index of thyroid gland failure. Hyperthyroidism is associated with increased serum T4, T3, and free T4. About 5% of patients have a selective increase in T3 secretion: T3 thyrotoxicosis. In these, serum T4 is normal but serum T3 is elevated. An absent TSH response to thyrotropin-releasing hormone (TRH) is the hallmark of hyperthyroidism due to suppression of anterior pituitary TSH secretion.

Full Text Links

Find Full Text Links for this Article


You are not logged in. Sign Up or Log In to join the discussion.

Trending Papers

Remove bar
Read by QxMD icon Read

Save your favorite articles in one place with a free QxMD account.


Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"