Bio L3 Thyroid Tests Flashcards

1
Q

Serum TSH test

A

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

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2
Q

How does TBG affect T3 & T4 tests?

A

Only free hormones can be measured, hence if TBG is high it would mask hyperthyroidism by binding the excess T4

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3
Q

Is T3 or T4 better at diagnosing hyperthyroidism? Why?

A

T3 because it increases earlier, some cases have only high T3 (toxicosis)
T3 is used to monitor therapy of hypothyroidism

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4
Q

What is the first line test in thyroid disease?

A

Total Serum T4

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5
Q

What is T3 resin uptake?

A

Indirect method to measure TBG abnormalities. It measure empty TBG binding sites

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6
Q

Drugs that raise TBG?

A

Estrogens & phenothiazines (anti-psychotic)

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7
Q

Drugs that reduce TBG?

A

Androgens, corticosteroids, salicylates phenylbutazone (NSAID), steroids

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8
Q

Which diseases increase TBG?

A

Chronic liver failure, acute intermittent porphyria

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9
Q

Diseases that reduce TBG?

A

Acromegaly, nephrotic syndrome, malnutrition

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10
Q

TRH stimulation test procedure?

A

200 TRH is given and TSH is measured before and 20 & 60 minutes after, TSH shoul peak at 30 min

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11
Q

TRH Stimulation Test diagnostic significance?

A

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.

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12
Q

How is rT3 measured

A

From serum T4, 5 & 5’ deiodimase activities

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13
Q

Most useful test to determine thyroid autoimmune disease ?

A

Anti-TPO Abs

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14
Q

Elevated anti-TPO in what conditions?

A

Hashimoto thyroiditis and Grave’s

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15
Q

T4 is normal, TSH are undetectable what’s the condition?

A

T3 thyrotoxicosis

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16
Q

TSH slightly elevated, fT4 is normal, next step?

A

Test T4 and TSH after 2-3 months

17
Q

If TSH is still elevated after 2-3 months, whats the next step ?

A

Measure thyroid autoantibodies titres

18
Q

Sick euthyroid syndrome

A

TSH, T3, T4 are all normal, suggests secondary hypothyroidism caused by hypopituitarism
However, normal cortisol =normal pituitary

19
Q

How to diagnose early grave’s disease?

A

T3 toxicosis

20
Q

Effect of iodine deficiency?

A

Hypothyroidism & more T3 than T4

21
Q

What inhibits 5’ deiodinase?

A

Stress of surgery, anesthesia