Thyroid Function Tests

Question 1

what is the test of choice for dogs with hypothyroidism? can you always trust its results?

Answer 1

A total T4 is the test of choice for screening a dog for hypothyroidism and is very sensitive but not specific so false positives are common. Autoantibodies, illness and drugs can falsely lower or increase the total t4 and should be considered when interpreting

Question 2

If you perform a total t4 and are unsure if the dog is truly hypothyroid, what test should you perform and why?

Answer 2

a Free T4 would be the next step because its highly sensitive and specific in most instances as most autoantibodies don’t effect free T4 as they do a total T4

Question 3

in a hypothyroid dog what would you expect the TSH value to be in relation to the total T4?

Answer 3

the TSH should be elevated in about 60-75% of cases but isn’t very specific, T4 and TSH are usually inverse of eachother

Question 4

what value is commonly elevated on blood chemistry of hypothyroid patients? CBC?

Answer 4

hypercholesterolemia (75%) on chemistry and mild non regenerative anemia (25%) on cbc

Question 5

what are some general signs of hypothyroidism in dogs?

Answer 5

Middle aged, lethargy/weakness, obesity, exercise intolerance, alopecia, seborrhea, myxedema, cardiovascular and neurologic abnormalities

Question 6

what breeds have lower T4 and fT4?

Answer 6

sighthounds

Question 7

why might a total t4 be elevated even with high clinical suspicion of hypothyroidism?

Answer 7

1. interference with autoantibodies to T3/T4 that may be a marker of autoimmune thyroiditis
2. drugs
3. breeds
4. NTI

Question 8

lymphocytic thyroiditis

Answer 8

Autoimmune inflammation that causes atrophy of the thyroid when lymphocytes and plasma cells produce antibodies directed at thyroglobulin, colloid, TT3 and TT4. This is the most common cause of hypothyroidism but can cause an elevation of total t4

Question 9

lymphocytic thyroiditis is supported by high __ and __

Answer 9

T3 and T4

Question 10

what is the most common cause of hypothyroid cases?

Answer 10

autoimmune thyroiditis is the cause of 50% of hypothyroid cases

Question 11

treatment of hypothyroidism

Answer 11

Levothyroxine once per day

They should see improved clinical signs relatively quickly with the exception of dermatological issues. The dog should be rechecked in 8 weeks and post pill testing (T4 peaks 4 hours post tx to normal or slightly about the normal range)

Question 12

thyroid slip

Answer 12

a palpable nodule in the thyroid area associated with the diagnosis of hyperthyroidism

Question 13

in hyperthyroid cats, what percent will have a high T4?

Answer 13

90%, if T4 is at the upper end of the RR then a NTI or early disease may be present making it appear lower/be suppressed

Question 14

what enzymes are elevated in 90% of hyperthyroid cats?

Answer 14

liver enzymes mild to moderately

Question 15

clinical signs of hyperthyroidism in cats

Answer 15

hyperactivity, weight loss with normal appetite, PU/PD, tachycardia, vomiting, patchy alopecia

Question 16

what is diagnostic of hyperthyroidism in cats?

Answer 16

Elevated fT4 when total T4 is in the upper 25% of the RR

Question 17

T/F: TSH is supressed in 98% of cats

Answer 17

T