Thyroid

Question 1

Hyperthyroid signalment

Answer 1

Common in cats
Usually only see as a malignant thyroid tumor in dogs

Question 2

Hypothyroidism

Answer 2

Markedly decreased tT4 and fT4 is diagnostic for primary, secondary or tertiary

Question 3

Primary hypothyroidism hallmark

Answer 3

Decreased fT4 and increased TSH

Question 4

Secondary hypothyroidism

Answer 4

Deficiency in secretion of TSH from pituitary

Question 5

Tertiary hypothyroidism

Answer 5

Deficiency of TRH secretion from hypothalamus

Question 6

Sick euthyroid

Answer 6

Hypothyroxemia due to non thyroidal diseases (Neoplasia, hyperadrenocorticism, infammatory disease, drugs)

Question 7

Processes of sick euthyroid

Answer 7

-Decreased protein bound
-Inhibition of TSH secretion
-Inhibition of T4 production

Question 8

Measuring tT4

Answer 8

Rule in hyperthyroidism in cats
Rule out hypothyroidism in dogs
Can be suppressed in non thyroidal illnesses

Question 9

Increased tT4

Answer 9

Increased production by thyroid neoplasia
-Thyroid adenoma or adenocarcinoma
-Positive interference by T4AA in dogs (false increase)

Question 10

Decreased tT4

Answer 10

-Decreased production: Primary is the most common (secondary and tertiary are rare
-Multifactorial: Sick thyroid, drugs

Question 11

tT4 in healthy dogs

Answer 11

Much lower than cats and horses so must use a lower detection limit to measure normal and decreased

Question 12

Why does T4AA cause positive interference

Answer 12

Binds to labelled T4 in the test tube so there is less competition for those binding sites and when you measure the radioactivity of the sample, it makes it look like there is more pt T4 than there really is

Question 13

tT4 test

Answer 13

Competitive binding assay
Combine pt serum with a known amount of labelled T4 and they compete for binding spots on antibodies in the tube. The more pt T4 the less labelled T4 that binds and vice versa

Question 14

TSH measurement

Answer 14

Always interpret with tT4 and or fT4
Use to differentiate cause of hypothyroidism
TSH usually increased if primary

Question 15

Increased TSH with decreased TT4 and fT4

Answer 15

Almost 100% specific for primary hypothyroidism

Question 16

Autoantibody titers

Answer 16

Used to diagnose autoimmune thyroiditis not thyroid function

Question 17

Thyroglobulin autoantibody (TgAA)

Answer 17

Immune response to thyroglobulin due to damaged cells releasing and reaction as a foreign protein

Question 18

Decrease tT4, TSH WRI and positive TgAA

Answer 18

Supports hypothyroidism

Question 19

T4AA

Answer 19

Dogs with lymphocytic thyroiditis recognize T4 as foreign
More important because of test interference

Question 20

fT4

Answer 20

1% of serum thyroxin but good for diagnostics
Less suppression by non thyroid diseases and drugs

Question 21

fT3 WRI

Answer 21

Rule out hypothyroidism in dogs

Question 22

Assays for fT4

Answer 22

Equilibrium dialysis
Serum sample filtered through membrane that only fT4 can pass through ( not protein or antibodies) and then measure

Question 23

Increased fT4

Answer 23

Increased production by thyroid neoplasia
Often seen in concurrence with tT4

Question 24

Decreased fT4

Answer 24

Usually in primary hypothyroidism with decreased tT4