Thyroid Labs & Studies Flashcards
briefly, what does the thyroid hormone (T3 and T4) do within the body when active
what types of pts. are you suspecting to get thyroid studies one
Thyroid Hormones: play a vital role in metabolism of the body
- affect brain function, heart rate, breathing
- digestive rate
- liver function
- MSK growth and development
- reporductive abilities
Order thyroid studies in
- those with clinical exam findings (exopthalmos)
- edema
- a fib
- hyper or hypometabolic states
- gout
- DM or autoimmune conditions
- psychiatric complaints
- CAD
- adrenal insufficiency
Hyper: overactive
- weight loss
- heat intolerance
- tremor/palpatations
- anxiety
- increased bowl movements
- SOB
- goiter
- amenorrhea
Hypo: less active
- weight gain
- cold intolerance
- dyspnea on exertion
- constipation
- dry skin
- edema
- hoarseness
- menorrhagia
- myalgias, parasthetias, arthraligas
Populations which should be screenedwith thyroid labs
populations to screen
- autoimmune thyroid disease in 1st degree relatives
- those who have had previous neck raditaion (risk for thyroid CA)
- past history ot thyroid surgery/issues
- new medication therapy: amioderone and lithium
- pregnant women will present similar to general population- TSH should be done at the first prenatal visit
Thyroid Labs
Thyroglobulin
Thyroglobulin: the protein compound to which iodine is bound to in order to make active thyroid hormone
- used in thyroid synthesis
monitored in those post-surgical thyroidectomy: an increase can trigger a recurrance of cancer
- monitor every 3-6 months = first 2 years
- then every 6-12 months
Thyroid Labs
Thyroxine-binding globulin
Thyroxine-binding globulin: the protein to which thyroid hormone binds to to circualte within the blood
- the transport proteins for the hormone
- almost ALL the T3 and T4 are circualting bound to thyroxine-binding globulin
not very significant to monitor
but, if elevated T3 and T4 in the absence of other symptoms of disease, can be importnat to check to see how much is avalible and bound to T3 an T4: amount bound means there is less avalible to do its job (work freely) and thus, TSH could be elevated attempting to compenstate
Elevated in
- pregnant
- liver disease
- hypothyroid
- porphyria
Decreased in
- hyperthyroid
- cushings
- malnutrtion
- acromegaly
- CKD (nephrotic syndrome)
- inherited
Thyroid Labs
Thyroid Stimulating Hormone
meds which can impact proper labs
TSH: the most commonly ordered lab for thyroid
- results are reliable and not affected by proteins in the body
- the first lab ususally ordered to determine if there is a derrangement in the thyroid function
- used to follow-up for levothroyxine treatment
can be delayed in acute changes to thyroid function: as its secreted by pituitary in response to thryoid
Medications impacting
- ASA: asprin
- steroids (most common, in chronic low dose)
- st johns wort
- some diuretics
- thyroid meds
- Biotin: hold 2 days priot to labs if > 10 then hold more
Diagnosis & Monitoring for hypothyroidism
Diagnosis
- elevated TSH + low T4 free
- or subclinical: elevated TSH but normal FT4
Monitoring
- TSH after 4-8 weeks of meds while adjusting dose
- then TSH at 6 months then yearly
- drugs: this can impact levothroxyine efficacy if started –> aluminum hydroxide, amioderone, bile acid sequesterants, calcium
Diagnosis of Hyperthyroidism
Diagnosis
- Low TSH and High FT4
- subclinical: low TSH and normal FT4
Thyroxine (T4)
total
free
Total T4: bound and free levels
- can be good to see thyroid gland output of T4; good at seeing acute changes
- but the concentration of free is highly dependent and variable depending on the amount of protein (thyroid binding globulin) which varies with liver function
Free T4
- the biologically active form of T4: but the prohormone still to the active form of T3!
- monitor free T4 in central hypothyroidism: pituitary adenomas since TSH will be an issue
- levels of free can flucutate with bind protein levels
Triiodothyronine (T3)
T3: relaibale: showing the active hormone
- changes fast with thyroid activity changes
- disproportinuately overproduced during thyrotoxicosis
- majority of T3 is actually produced in peripheral tissues during converstion from T4 to T3 so T4 is often a better marker of thyroid
FT4I: free thyroxine index
when is it used
T3 uptake test
- largely unnecessary in practice
- uses thyroid binding index or T3 uptake to help assess if the binding proteins are the issue
- not reliable at extremes
calculated:
Free T4 index = total T4 x T3 uptake
T3 uptake
- done to distinguish the thyroxing binding globulin excess/deficiency from hyper or hypothyroidism
- determines if its a thyroid issue or if its a protein issue
if its a protein issue: the T4 index will be normal: since the production of T4 is not an issue
if hypo: all will be low
if hyper: all will be high
Indications for a thyroid US
- to classify and monitor thyroid nodules
- surgical planning
- guided FNA
- assess lymph nodes
- helps in thyrotoxicosis and thyromegaly
- screen/survey in cancer
- fetal evaulation
an US is first line over CT for suspected tyroid nodule or a nodule with goiter
Benign and cancerous characteristics of nodules on thyroid US
Benign
- isoechoic: normal thyroid tissue echoic
- hyperecoic: brighter
- simple cyst looking
Cancerous
- hypoecoic: darker
- punctate ecogenic foci (microcalcifications)
- taller than it is wide
- infiltrative margins
- (absence of the above findings does NOT rule out CA)
Thyroid Nuclear Study
when is it done and why
- uses radioactive tracers to watch the uptake to the thyroid: indicate activity
- looked at 6 hours and then at 24 hours
- not often done, but can be helpful
- more uptake = hyperactive thyroid
- less uptake = hypoactive thyroid
hyperfunction: less likely cancer
Thyroid FNA
indications: US features suggestive for cancer
- want to make sure theyre not a bleed risk pt, and have adequate platelets since thyroid is vascular
- based on US findings: TIRADS score (from radiology0 will indicate which nodules should get biopsied
- ATA guidelineS: more lienent for thyroid nodule biopsy (if pt. anxious and wanting FNA)
Who gets one
- solid, hypoechoic nodules ( > 1.5 cm)
- solid hypoechoic 1-1.5 cm & have the calcifications, taller > wider, irregular margins, etc.
- any node > 1 cm is usually palpable by the pt.
- if strong family history of cancer, syndromes assocaited with CA or history of childhood radiation ot area = FNA indicated
Risks of an FNA thyroid
rare but: bleeding, pain, swelling non-diagnostic sample
super rare: laryngeal nerve palsy
- cerivcal radiculopathy
- dysphagia,
- hematoma
- fibervasucalr mass
- needle track seeding of tumor
