Thyroid, Adrenal, and Pituitary Flashcards
In euthyroid sick (decide if increased or decreased):
TT4-
fT4-
rT3-
TT4- decreased
fT4- decreased
rT3- increased
Why is TT3 not very good for diagnosing thyroid diseases?
mostly comes from outside the thyroid
T or F: T4 is extremely high in birds and reptiles.
F- it’s extremely low b/c not as many binding proteins
What is a scenario where a dog w/normal TT4 could really have hypothyroidism?
10% have anti-T4 antibodies that can cause T4 to increase and mask hypothyroidism
Indicate a decrease, increase or N- For primary hypothyroidism: TT4- fT4- TSH-
TT4- decreased
fT4- decreased
TSH- increased
What breeds have lower T4 and fT4?
sighthounds and basenjis
What is the interp:
TSH- increased
TT4- decreased
fT4- decreased
100% specificity for hypothyroidism
Interpret:
TSH- N
TT4- decreased
fT4- decreased
might still be hypothyroid but is in the category of that 25%-33% of dogs with hypothyroidism and no increase in TSH
Interpret:
TSH- decreased
TT4- decreased
fT4- decreased
secondary hypothyroidism (only 5% of cases)
What does thyroxine do to TSH?
decreases it (can use to monitor hypothyroid treatment)
Interpret TRH response test results:
pre-TRH: TT4 in RI
post-TRH: double the baseline
Normal cat (not hyperthyroid)
When would you consider doing a TRH response test?
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
Interpret the TSH response test results:
pre TSH TT4: below RI
post TSH TT4: increased 2x or more from baseline
Euthyroid sick
Interpret the TSH response test:
TT4 pre-TSH: below RI
TT4 post-TSH: below RI
hypothyroid
T or F: The presence of antibodies against TT4, TT3 or Tg confirm hypothyroidism.
False- just means there is lymphocytic thyroiditis and it may not ever develop into true hypothyroidism.
What is the purpose of running a TSH?
to differentiate between primary hypothyroidism, secondary hypothyroidism, and euthyroid sick.
In a dog with suspected hypothyroidism that has normal or high T4, what should be considered?
the presence of antibodies against T4 and/or Tg
Interpret TRH response test results:
pre-TRH: TT4 in RI
post-TRH: TT4 in RI
Hyperthyroid (neoplastic cells don’t respond to TSH increase)
How does size and unilateral vs bilateral status of a thyroid tumor relate to prognosis in dogs?
80% that are big enough to be found clinically are malignant
bilateral 16x more likely to met than unilateral
What is the most common biochemical abnormality in cats with hyperthyroidism?
increased ALP (70%)
What should you do if you suspect hyperthyroidism in a cat but the TT4 is normal?
run a fT4 and/or a TRH response test
Fructosamine is higher or lower in hyperthryoid cats than normal cats?
lower (b/c accelerated albumin turnover)
What % of hyperthyroid cats will have a normal TT4?
5-10%
Suspect hyperthyroidism and get a decreased TT4. Interp?
not hyperthyroidism (99% sure)
What % of cats with hyperthyroidism have an increased fT4?
98%
What should you do if you get an increased TT4 in a dog?
run a test for thyroid antibodies to rule out thyroiditis that might be causing falsely increased TT4
Why can’t you use fT4 alone to diagnose hyperthryoidism?
because you can have increased fT4 without an increased TT4 in euthyroid sick cats
What is the concept of the TT3 suppression test?
give TT3 orally to see if it suppresses TSH secretion which decreases serum TT4
Interpret results of a TT3 suppression test:
TT4 pre: in RI
TT4 post: below RI
normal cat (not hyperthyroidism)
Why won’t a hyperthyroid cat have suppressed TSH levels with the T3 suppression test?
because their tumor is secreting TT4 and TT3 which already causes a suppressed TSH level (can’t suppress any further)
Interpret results of a TT3 suppression test:
TT4 pre: in RI
TT4 post: in RI
hyperthyroid (not suppressing)
What is the drawback of using the TRH response test?
TRH admin can cause tachycardia, salivation, tachypnea
What is the drawback of using the TSH response test?
bovine TSH isn’t available anymore and human TSH is expensive
Interpret endogenous TSH test results:
TT4: N
fT4: N
eTSH: decreased
hyperthryoidism (only use when you suspect hyperthyroidism but the screening tests aren’t definitive)
In a dog with hypothyroidism that has a high TT4 from antibodies, will the fT4 be affected?
no not usually affected so should be low
Myxedema is uncommon but pathognomonic for what?
hypothyroidism
What is unique about sighthound TT4?
it is low normally so need to use a different test to diagnose hypothyroidism in them
What would you expect in a case of goiter?
TT4-
fT4-
TSH-
TT4- decreased
fT4- decreased
TSH- increased
