Thyroid, Adrenal, and Pituitary

Question 1

In euthyroid sick (decide if increased or decreased):
TT4-
fT4-
rT3-

Answer 1

TT4- decreased
fT4- decreased
rT3- increased

Question 2

Why is TT3 not very good for diagnosing thyroid diseases?

Answer 2

mostly comes from outside the thyroid

Question 3

T or F: T4 is extremely high in birds and reptiles.

Answer 3

F- it’s extremely low b/c not as many binding proteins

Question 4

What is a scenario where a dog w/normal TT4 could really have hypothyroidism?

Answer 4

10% have anti-T4 antibodies that can cause T4 to increase and mask hypothyroidism

Question 5

Indicate a decrease, increase or N-
For primary hypothyroidism:
TT4-
fT4-
TSH-

Answer 5

TT4- decreased
fT4- decreased
TSH- increased

Question 6

What breeds have lower T4 and fT4?

Answer 6

sighthounds and basenjis

Question 7

What is the interp:
TSH- increased
TT4- decreased
fT4- decreased

Answer 7

100% specificity for hypothyroidism

Question 8

Interpret:
TSH- N
TT4- decreased
fT4- decreased

Answer 8

might still be hypothyroid but is in the category of that 25%-33% of dogs with hypothyroidism and no increase in TSH

Question 9

Interpret:
TSH- decreased
TT4- decreased
fT4- decreased

Answer 9

secondary hypothyroidism (only 5% of cases)

Question 10

What does thyroxine do to TSH?

Answer 10

decreases it (can use to monitor hypothyroid treatment)

Question 11

Interpret TRH response test results:
pre-TRH: TT4 in RI
post-TRH: double the baseline

Answer 11

Normal cat (not hyperthyroid)

Question 12

When would you consider doing a TRH response test?

Answer 12

used instead of TSH to ID hypothyroid in dogs or hyperthyroidism in cats when other tests aren’t clear and can’t wait weeks to retest

Question 13

Interpret the TSH response test results:
pre TSH TT4: below RI
post TSH TT4: increased 2x or more from baseline

Answer 13

Euthyroid sick

Question 14

Interpret the TSH response test:
TT4 pre-TSH: below RI
TT4 post-TSH: below RI

Answer 14

hypothyroid

Question 15

T or F: The presence of antibodies against TT4, TT3 or Tg confirm hypothyroidism.

Answer 15

False- just means there is lymphocytic thyroiditis and it may not ever develop into true hypothyroidism.

Question 16

What is the purpose of running a TSH?

Answer 16

to differentiate between primary hypothyroidism, secondary hypothyroidism, and euthyroid sick.

Question 17

In a dog with suspected hypothyroidism that has normal or high T4, what should be considered?

Answer 17

the presence of antibodies against T4 and/or Tg

Question 18

Interpret TRH response test results:
pre-TRH: TT4 in RI
post-TRH: TT4 in RI

Answer 18

Hyperthyroid (neoplastic cells don’t respond to TSH increase)

Question 19

How does size and unilateral vs bilateral status of a thyroid tumor relate to prognosis in dogs?

Answer 19

80% that are big enough to be found clinically are malignant

bilateral 16x more likely to met than unilateral

Question 20

What is the most common biochemical abnormality in cats with hyperthyroidism?

Answer 20

increased ALP (70%)

Question 21

What should you do if you suspect hyperthyroidism in a cat but the TT4 is normal?

Answer 21

run a fT4 and/or a TRH response test

Question 22

Fructosamine is higher or lower in hyperthryoid cats than normal cats?

Answer 22

lower (b/c accelerated albumin turnover)

Question 23

What % of hyperthyroid cats will have a normal TT4?

Answer 23

5-10%

Question 24

Suspect hyperthyroidism and get a decreased TT4. Interp?

Answer 24

not hyperthyroidism (99% sure)

Question 25

What % of cats with hyperthyroidism have an increased fT4?

Answer 25

98%

Question 26

What should you do if you get an increased TT4 in a dog?

Answer 26

run a test for thyroid antibodies to rule out thyroiditis that might be causing falsely increased TT4

Question 27

Why can't you use fT4 alone to diagnose hyperthryoidism?

Answer 27

because you can have increased fT4 without an increased TT4 in euthyroid sick cats

Question 28

What is the concept of the TT3 suppression test?

Answer 28

give TT3 orally to see if it suppresses TSH secretion which decreases serum TT4

Question 29

Interpret results of a TT3 suppression test: TT4 pre: in RI TT4 post: below RI

Answer 29

normal cat (not hyperthyroidism)

Question 30

Why won't a hyperthyroid cat have suppressed TSH levels with the T3 suppression test?

Answer 30

because their tumor is secreting TT4 and TT3 which already causes a suppressed TSH level (can't suppress any further)

Question 31

Interpret results of a TT3 suppression test: TT4 pre: in RI TT4 post: in RI

Answer 31

hyperthyroid (not suppressing)

Question 32

What is the drawback of using the TRH response test?

Answer 32

TRH admin can cause tachycardia, salivation, tachypnea

Question 33

What is the drawback of using the TSH response test?

Answer 33

bovine TSH isn't available anymore and human TSH is expensive

Question 34

Interpret endogenous TSH test results: TT4: N fT4: N eTSH: decreased

Answer 34

hyperthryoidism (only use when you suspect hyperthyroidism but the screening tests aren't definitive)

Question 35

In a dog with hypothyroidism that has a high TT4 from antibodies, will the fT4 be affected?

Answer 35

no not usually affected so should be low

Question 36

Myxedema is uncommon but pathognomonic for what?

Answer 36

hypothyroidism

Question 37

What is unique about sighthound TT4?

Answer 37

it is low normally so need to use a different test to diagnose hypothyroidism in them

Question 38

What would you expect in a case of goiter? TT4- fT4- TSH-

Answer 38

TT4- decreased fT4- decreased TSH- increased