Answer:
Dear
Abbey,
Low or
undetectable levels of TSH are present in patients with hyperthyroidism.
Each
laboratory defines its own normal ranges but using the SimulTRAC FT4/TSH
Solid Phase Component System, Hyperthyroid Ranges for
TSH:
0.05 - 0.56 µU/mL
Commonest
cause of reduced (<0.1 mU/L) Thyrotropin and normal FT4 or FT3
is taking thyroxine. Less commonly, is sub clinical primary hyperthyroidism
(elderly). Often a multinodular goiter is present.
An abnormal
thyrotropin result will necessitate additional tests - probably FT4
or FT3 estimates, in the first instance. More sophisticated investigations
(e.g. anti-TPO, radioiodine uptake) may be ordered by a thyroid-specializing
endocrinologist.
Low and
high thyrotropin levels were associated with an increased risk of
incident Alzheimer's disease in women but not in men.
Researchers
found that women with the lowest (less than one milli-international
unit per liter) and highest (more than 2.1 milli-international units
per liter) levels of thyrotropin had more than a twofold increased
risk of Alzheimer's.
Thyrotropin
is known also as thyroid stimulating hormone (TSH). Thyrotropin (or,
if you prefer, TSH) promotes the growth of the thyroid gland in the
neck.
35 85-year-old
men and women who were found to have low thyrotropin levels were followed
for three years. Eighteen were not receiving thyroid hormone treatment,
and no cause could be found for their low thyrotropin levels. They
did not suffer from hyperthyroidism, in which excess levels of thyroid
hormones inhibit the production of thyrotropin
Low thyrotropin
levels in the elderly are not necessarily a sign of hyperthyroidism
or impending death. Better diagnostic tests will help to identify
elders who are truly hyperthyroid.
