Thyroid Studies Flashcards
TSH
responsible for the synthesis and secretion of T3 (triiotathyronine) /T4 (thyroxine) -best screening test for thyroid function
T3 and T4 function
assist with cellular respiration and metabolism
TRH
thyrotropine releasing hormone (comes from hypothalamus)
Thyroid feedback systems are present in the
hypothalamus and anterior pituitary
TSH screening test normal value
normal 0.5-5.5 mlU/L -taken in red or marble top -not useful if they have had surgery on or damage to the anterior pituitary
interfering factors in the TSH screening
radioisotope administration severe illness drugs
increased TSH because of drugs could be
lithium
potassium iodide
TSH injection
decreased TSH because of drugs could be
ASA
NSAIDS
heparin
corticosteroids (Prednesone in the case of RA)
Thyroxine (T4)
More abundant thyroid hormone
Triiodothryonine (T3)
thyroid hormone that is secreted in lesser amounts, but that is more metabolically active
-is T4 less one iodine
Thyroid binding globulin (TBG)
protein that binds to T3/T4
- free T4 and T3 is what actually does the work
- produced in the liver
- free hormone levels are not altered by changes in TBG (stays constant)
- changes in TBG may affect total thyroid hormone levels
free T4 test
2nd test that you would order in a thyroid work-up
increase in TBG might be because of
high estrogen states (OCP, pregnancy, hormone replacement therapy)-gives total T4 elevation
infectious hepatitis (causes inflammation and churns out extra hormone)
genetic TBG excess
decrease in TBG might be because of
liver disease (cirrhosis)
malnutrition
protein losing nephropathy
androgens
estrogen deficiency
major stress
thyroid screening tests
- TSH
- Free T4
***Need to pay attention to whether it says FREE otherwise assume it is total
thyroglobulin work up
indicated for someone who has a thyroid tumor
used as a tumor marker
- protein that is made by the thyroid gland
- elevated levels indicate residual thyroid tissue
increased TSH level indicates
hypothyroidism
-thyroid is not responding to the TSH and pituitary is compensating by making more
>5.5 mgU/dl
decreased TSH level indicates
hyperthyroidism
- pituitary is reading that thyroid hormone levels are high and decreases secretion of TSH
- <0.5 mgU/dl
Two tests that are used to diagnose autoimmune disease
- thyroid stimulating immunoglobulin (Graves dx)
- thyroid antibodies (Hashimotos)
- anti-TPO antibodies-most sensitive
- antithyroglobulin antibodies-less sensitive
