TSH is usually low in hypothyroidism secondary to pituitary disease, but in some patients, abnormally glycosylated and poorly active TSH is secreted and measured by RIA with levels up to 8 or even 10mu/l. Values above 5mu/l are usually indicative of some degree of thyroid failure, and in overt primary hypothyroidism, values may be in the range of 10ΓÇôl00mu/l or higher. A normal TSH value excludes primary hypothyroidism, provided that the hypothalamopituitary axis is intact.
