Final

Question 1

what are the primary functions of the thyroid gland

Answer 1

• Maintain metabolic rate
• Thermogenesis
• Stimulate growth and maturation
• Stimulate heart rate, cardiac output, blood flow
• Hormones work to increase gene transcription for proteins that serve these functions
• Calcium regulation

Question 2

what do parafolliclar cells or C cells do

Answer 2

Produce calcitonin which in turn prevents hypercalcemia

Question 3

which is the active form? T3 or T4, and what is it’s function

Answer 3

T3 acts to increase metabolic rate, and the production is stimulated by TSH

Question 4

what is T3 and T4 bound to in circulation

Answer 4

• T3 and T4 bound to plasma proteins (primarily specific globulins, some albumin) in circulation.
• Only unbound (free) T3 and T4 enter cells and bind to
nuclear receptors.

Question 5

what are the the tests that can assess thyroid state and function? (there are 9)

Answer 5

• Serum total T4 and
free T4 concentrations
• Serum total T3 and
free T3 concentrations
• TSH concentration
(endogenous)
• TSH stimulation test
• TRH stimulation test
• T3 suppression test
• Autoantibodies
• Scintigraphic imaging
• Biopsy of thyroid

Question 6

why should you not use a human assay to measure T4?

Answer 6

Dog T4 runs below limits of detection for many analyzers

Question 7

which form of T4 is found in the highest concentration

Answer 7

Protein bound T4

Question 8

Is a low T4 diagnostic of hypothyroidism? if so/not why?

Answer 8

• EXTRATHYROIDAL DISEASE CAN DECREASE VALUES!

– Drugs too: Glucocorticoids, sulfonemides,
phenobarbitol, NSAIDS

Question 9

what does a thyroid autoantibody test tell us?

Answer 9

Suggestive of thyroid destruction associated with

lymphocytic thyroiditis

Question 10

what are 3 reasons you would have an increased T4 test result

Answer 10

– Hyperthryroidism
– Supplementation
– Interfering antibodies

Question 11

what drugs can cause a False decreased T4 tests leading you to think your patient my be hypothyroid

Answer 11

• Glucocorticoids
• Sulfonamides
• Phenobarbital
• NSAIDS

Question 12

where does TSH come from

Answer 12

pituitary

Question 13

what other test should be run with a T4? and what Dz does it aid in diagnosing?

Answer 13

Serum endogenous TSH, helps with hypothyroidism

Question 14

what does the TRH test measure? and what can it be used for

Answer 14

T4 production, and aid in diagnose in hyperthyroidism in cats, or hypothyroidism in horses

Question 15

what is the T3 suppression test used for? and how do you interpret it?

Answer 15

Used to evaluate patients for hyperthyroidism
– Measure baseline T4 and T3, then give dose of T3
– Measure serum T4 and T3 after dosing
• If T4 decreased to less than 1.5 ug/dl or greater than 50% suppression of baseline, then euthyroid
• If T4 the same (not responding to T3 feedback),
then hyperthyroidism is present
• Note that if T4 is already increased in patients
suspected of hyperthyroidism, this is not necessary
to perform

Question 16

what are some common clinical signs for hypothyroidism

Answer 16

– Truncal alopecia
– Weight gain without polyphagia
• Decreased metabolic rate
– Neuromuscular signs
• Hypotonia, hindlimb paresis, weakness
– Lethargy

Question 17

what are some blood tests abnormalities found in hypothyroid patients

Answer 17

• Normocytic normochromic anemia: (20-50%)
– ↓thyroid hormone → ↓ EPO, Fe, and TIBC
• Hypercholesterolemia: (70-80%)
– ↓ conversion to bile acids
– ↓ fecal excretion
• CK increased in ~10% (rarely)

Question 18

give a brief over view of nonthyroidal illness syndrome

Answer 18

• Nonthyroidal illness can lower serum total T4 and T3.
• Multifactorial mechanisms
– Some drugs, such as glucocorticoids, can alter thyroid hormone concentrations.
• About 10% of euthyroid sick dogs will have low free T4, and about 25% of hypothyroid dogs will have normal TSH, so the tests aren‘t perfect!