Bio L3 Thyroid Tests Flashcards
Serum TSH test
1) most useful in primary hypothyroidism
2) A rise indicates no feedback inhibition due to hypothyroidism
3) In hyperthyroidism: TSH is subnormal (feedback inhibition)
4) differentiation of pituitary & hypothalamic hypothyroidism
How does TBG affect T3 & T4 tests?
Only free hormones can be measured, hence if TBG is high it would mask hyperthyroidism by binding the excess T4
Is T3 or T4 better at diagnosing hyperthyroidism? Why?
T3 because it increases earlier, some cases have only high T3 (toxicosis)
T3 is used to monitor therapy of hypothyroidism
What is the first line test in thyroid disease?
Total Serum T4
What is T3 resin uptake?
Indirect method to measure TBG abnormalities. It measure empty TBG binding sites
Drugs that raise TBG?
Estrogens & phenothiazines (anti-psychotic)
Drugs that reduce TBG?
Androgens, corticosteroids, salicylates phenylbutazone (NSAID), steroids
Which diseases increase TBG?
Chronic liver failure, acute intermittent porphyria
Diseases that reduce TBG?
Acromegaly, nephrotic syndrome, malnutrition
TRH stimulation test procedure?
200 TRH is given and TSH is measured before and 20 & 60 minutes after, TSH shoul peak at 30 min
TRH Stimulation Test diagnostic significance?
1) In hyperthyroidism, no TSH elevation due to feedback inhibition
2) In 1ry hypo: Exaggerated TSH elevation
3) In 2ry hypo: no response to pituitary abnormalities, sluggish response (>60min) to hypothalamic.
How is rT3 measured
From serum T4, 5 & 5’ deiodimase activities
Most useful test to determine thyroid autoimmune disease ?
Anti-TPO Abs
Elevated anti-TPO in what conditions?
Hashimoto thyroiditis and Grave’s
T4 is normal, TSH are undetectable what’s the condition?
T3 thyrotoxicosis
