Thyroid Function

Question 1

(T/F) You can trust pretty highly that a dog with a normal total T4 does not have hypothyroidism.

Answer 1

(T, total T4 is very sensitive)

Question 2

There are lots of cases of false positive/negative (choose) total T4s in dogs.

Answer 2

(False positives, total T4 is very sensitive (low false negatives) and not specific (high false positives)

Question 3

(T/F) Free T4 is both highly sensitive and highly specific for detecting hypothyroidism in dogs.

Answer 3

(T, gold standard for diagnosis of hypothyroidism in dogs)

Question 4

TSH should be high/low (choose) in a hypothyroid dog.

Answer 4

(High)

Question 5

TSH should be high/low (choose) in a hyperthyroid cat.

Answer 5

(Low)

Question 6

(T/F) You can trust pretty highly that a dog with a normal TSH level does not have hypothyroidism.

Answer 6

(F, TSH is insensitive (lots of false negatives) but it is very specific so if it is positive (i.e. it is high) your patient for sure has hypothyroidism)

Question 7

What are some of the drugs that can falsely decrease total T4?

Answer 7

(Phenobarbital, sulfonamides, clomipramine, glucocorticoids, and NSAIDs)

Question 8

Besides drugs, what else can falsely decrease total T4?

Answer 8

(Non-thyroid illness and breed (specifically sight hounds))

Question 9

(T/F) Free T4 is not affected by T4 or T3 autoantibodies.

Answer 9

(Tricky, if I said Free T4 by equilibrium dialysis you could say true, all other assays for total or free T4 are inaccurate with autoantibodies)

Question 10

(T/F) It is rare for a hyperthyroid cat to have a total T4 concentration below the upper 25% of the reference range.

Answer 10

(T)

Question 11

(T/F) Free T4 can be falsely increased by non-thyroid illness in cats.

Answer 11

(T, 10-15% of cases, should never use free T4 as a stand alone test to diagnose hyperthyroidism in cats but if you pair an elevated fT4 with an upper 25% reference range TT4 = hyperthyroid cat)