Exam 5 Thyroid Flashcards by Abby Davis

what is a goiter

enlargement of thyroid gland

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hypothyroidism vs hyperthyroidism

hypo= inadequate thyroid hormone produciton

hyper= (thyrotoxicosis) over production of thyroid gland (hyperfunction of the gland)

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what is thyroditis

inflammation and destruction of the thyroid gland

ex: hashimoto

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name the cascade of thyroid hormone release

hypothalamus sends thyrotropin releasing hormone (TRH) to pituitary
pituitary sends thyroid stimulating hormone (TSH) to the thyroid via circulation
thyroid synthesizes and releases T3, T4 and Calictonin

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what acts as the negative feedback control for the thyroid hormones

T3 and T4 negative feedback to hypothalamus and pituitary

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what molecule is needed to produce thyroid hormones and must come from the diet

iodine

Ex: iodized salt

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is there more T4 or T3 secreted by thyroid

90% is T4

majority (80%) of T3 is created by the breakdown of T4
1/3 of T4 converted to T3

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what is the active form of T3/4

free T3/4- metabollically active

most is bound in proteins= not biologically available for use
thyroxine binding globuline (TBG (99% bound of T4 and 70% of T3)

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what comes on a thyroid panel

TSH

total T4

Free T3/4

Free T4 index - FT4I
(calculation that shows how much T4 there is relative to binding globulin)

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why order a thyroid panel

screen for thyroid disease / function of thyroid

monitor treatment of thyroid disorders

assess treatment of hypothyroidism (levothyroxine therapy)

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what is the most important test in evaluating thyroid function

TSH: more stable in the blood than T3/4

all newborns get this test to screen for congenital hypothyroidism

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if TSH is high what does this mean for T3 and T4

T3/4 will be low= hypothyroidism

pituitary recognizes low levels of - very sensitive
small changes in T4 cause large changes in TSH

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if TSH is low what does this mean for T3 and T4

T3/4 will be high= hyperthyroidism

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what is the goal of treating hypothyroidism (levothyroxine treatment)

provide adequate amount of exogenous T4 to minimize TSH secretion

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name some disorders that would increase TSH

HYPOthyroidism (congenital=cretinism and primary)

secondary HYPERthyroidism

pituitary adenoma

hashimoto’s thyroditis (autoimmune)

amiodarone/ dopamine antagonist= drugs

ectopic TSH producing tumors

TSH producing pituitary adenoma

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name some disorders that would decrease TSH

primary HYPERthyroidism

secondary HYPOthyroidism
- TSH near zero!!

Tertiary HYPO thyroidism

graves disease (autoimmune)- has no effect on TSH levels

glucocorticoids= drugs

excessive exogenous thyroid hormone

high levels of chronic gonadotropin

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what is primary hypothyroidism?

Secondary?

Tertiary?

primary: problem with thyroid
secondary: problem with pituitary
tertiary: problem with hypothalamus

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what is primary hyperthyroidism?

secondary?

primary: problem with thyroid
secondary: problem with pituitary

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in which disorder would TSH levels be near zero!!!

secondary hypothyroidism

what test is a direct measure of ALL circulating T4 (thyroxine)

total T4

this is protein bound and free

what are the critical values for Total T4

low: myxedema coma (under 2mcg/dl) due to hypothyroid, protein deficiency
- causes everything to slow down (hypotension, bradycardia, lethargy, etc)

high: thyroid storm (over 20 mvg/dl)
due to: hyperthyroid, too much iodine, high levothyroxine med, hepatitis
- causes hyper everything speeds it up
-hyperthermia, dehydration, shock

what test is not affected by fluctuations in TBG (thyroid binding globulin)

free T3/4

aka good for evaluating ppl with protein abnormalities

what test is most accurate indicator of T4 activity

free T4

used if not enough info from TSH

when should you check free T3 and T4

when suspect HYPER thyrodiism

need to rule out T3 toxicosis

what are thyroid immunoglobulins what are the types

IgG antibodies directed against thyroid receptor antigens 3 types 1. thyroid peroxidase (TPOAb or Anti-TBO= anti thyroid peroxidase antibody) 2. thyroglobulin (TgAb or Anti-Tg= anti thyroglobulin antibody) 3. TSH receptor Antibody (TRAb= anti TSH receptor antibody) - TSI - TBII

what would cause elevated TPOAb, TgAB

In order of most prevalence: hashimoto disease also graves, but most likely hashimoto other autoimmune diseases (type 1 diabetes) pregnancy goiter, isolated thyroid nodule, cancer

when should you order a TPOAb

to confirm Hasimotos (though you dont have to treat) or when pt with subclinical hypothyroidism to determine Tx plan (aka present with hypo but labs in normal range)

what thyroid test helps confirm graves

anti TSH receptor antibody (TRAb) checks for anti TSH receptor antibodies that would cause the continous firing of the receptor Two types TSI and TBII

what do nuclear thyroid scans do

measure thyroid funciton evaluate thyroid nodules find causes of hyperthyroidism / plan treatment for hyper/nodule see spread of thyroid cancer

when should you order a thyroid ultrasound

initial evaluation of a thyroid nodule!!!!!!!!!!!

what is radioactive iodine uptake and scan used for

determine if cancerous or not and if spread give the radioactive iodine and generally hypo = too little taken up and hyper= too much IN NODULES: HOT: high uptake- BENIGN COLD- low uptake CANCER-> nonfunctioning tissue

what can congenital hypothyroidism cause

irreversible damage to CNS developmental defects

symptoms of HYPO thyroid

fatigue cold intolerance dry skin constipation weight gain depression bradycardia menorrhagia

symptoms of HYPER thyrodisim

anxiety weakness tremor palpitation heat intolerance weight loss exophthalmia goiter

what do you do if you get a high TSH

first repeat TSH and check free T3/4 and index if normal= original = error if TSH still high= and free T4 low then hypothyroid if TSH high but free T4 normal= subclinical hypothyrodism same for low TSH but opp TSH low, high T4/T3= hyper

is HYPER or HYPO thyroidism more common

hypo = 95% of cases

what test would you order for pt with goiter

ultrasound + thyroid panel

if a pts TSH is low and Free T3/4 high what does this indicate

hyperthyroidism

what else could you order for a pt with hyperthyroidism and a goiter after the ultrasound

radioactive iodine uptake to determine if cancerous and then a biopsy cold means cancer = low uptake refer

what would you order for a pt complaining of flu like symptoms and an enlarged thyroid

thyroid panel

how long does it take for TSH levels to respond to levothyroxine treatment

4-6 weeks!!!!

what does high levels of thyroid peroxidase antibodies indicate (TPOAb)

hashimoto thyroiditis = elevated TPOAb

what is the first and primary test done to check thyroid

TSH most sensitive and specific screening lab

what condition would you exepct in person with HIGH TSH low TSH

high TSH= hypo low TSH= hyper

pt with thyroid nodule should have what initial study

ultrasound and thyroid panel