Thyroid Function Test Flashcards
most important in control of thyroid hormone levels
negative feedback loop
state of having normal thyroid gland function
euthyroid
how many % of gut absorbed inorganic iodide is trapped by the thyroid gland
20-40%
produced by basophil cells of the
anterior pitutary and principal stimulator for iodide transport into the thyroid
Thyrotropin or TSH
This may lead to depression of the thyroid’s iodine-trapping mechanism.
chronic excess of iodide
formed by the rough endoplasmic
reticulum of the follicular cells and is secreted into the follicular lumen
thyroglobulin
release of thyroid hormone is controlled by?
TSH
Iodinated thyroglobulin near the cell-colloid interface is hydrolyzed by these substances to release MIT, DIT, T3
and T4 into the cell
proteases and peptidases
True or False. The binding affinity for T4 is lower in the dog than the humans.
True
When T4 is released from the thyroid,
approximately how many % remains in the plasma?
40 percent
an expensive test for Grave’s disease
Serum thyroid stimulating immunoglobulin (TSI) or TSHR-Ab
marker for recurrent thyroid cancer, and also differentiate graves disease from factitious thyrotoxicosis
Serum thyroglobulin
Characteristics of Antithyroid peroxidase antibodies (TPO)
- organ specific and sensitive
- predict overt hypothyroidism
it is inactive and helpful to exclude central hypothyroidism
Reverse T3
useful in distinguishing t3 toxicosis from subclinical thyrotoxicosis
fT3
preferred test with TSH
FT4 assay
In dogs with normal total T4 concentrations the average calculated T3 not bound by T3 AA
147.2 +/- 144.4 ng/dl
dogs with low total T4 the value of average calculated T3 not bound by T3 AA
15.7 +/- 26.3 ng/dl
normal canine range of total T4 concentrations the average calculated T3 not bound by T3 AA
45-150 ng/dl
acts as an acceptor also involved in synthesis and later release of T4 and T3
Thyroglobulin
the biologically active form of T4 that can enter most cells of the body
Ft4
True or False. T4 and T3 are excreted in bile and urine.
True.
standard screening test for hypothyroidism in dogs
Basal tT4
an inheritable autoimmune disorder in many dog breeds, common cause of thyroid gland destruction and primary hypothyroidism in dogs at least 50% of cases
Lymphocytic thyroiditis
disease outside of thyroid hormonal system creates hypothyroxemia
Sick euthyroidism
Increase/Decrease. Effects of neoplastic, inflammatory, metabolic, endocrine disorders on tT4
Decreased.
It helps differentiate nonthyroidal illness from hypothyroidism when tT4 is decreased in dogs
Assessment of TSH and fT4
Diet contents that may produce lower tT4 in horses
protein, energy, copper, zinc
True or False. fT4 does not always mirror tT4
True.
Concurrently finding decreased tT4 and increased fT4 in cats, suggests?
Presence of sick euthyroid state.
Increase or Decrease. TSH levels in dogs with primary hypothyroidism.
Increased.
Poor or inadequate response to TSH stimulation was the gold standard for establishing this condition
thyroid hypoplasia (hypothyroidism)
assess the ability of the thyroid gland to produce T4 after being stimulated by TSH
TSH response test
indirectly assess thyroid function by causing the release of TSH that stimulates release of T4
TRH response test
TRH response test in not approved in these species
horses
TRH response test is not needed to diagnose hyperthyroidism in these species
Cats
a useful screening test for diagnosing hypothyroidism in dogs
Total T4 (Thyroxine) measurement
useful for diagnosis of true hypothyroidism and differentiating it from euthyroid sick condition
fT4 measurement
