Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Endocrinology > Thyroid labs and imaging > Flashcards

Thyroid labs and imaging Flashcards

1
Q

Thyroxine (T4)

A

greatest amount of thyroid hormone

- T4 must be converted to the active hormone T3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Triiodothyronine (T3)

A
  • most biologically active
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Calcitonin

A

produced in parafollicular cells (C cells) of the thyroid

  • involved in regulating blood levels of Ca and phosphate by inhibiting osteoclast activity
  • decrease resorption of Ca in the kidneys
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Thyroid hormone metabolism

A
  • thyroid hormones are poorly soluble in the plasma
  • 0.03% of T4 and 0.3% of T3 unbound
  • only free T3 and T4 can penetrate cellular membranes and exert biologic activity by interacting w/ nuclear receptors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Where is T4 converted to T3 at?

A
  • *liver, gut, skeletal muscle, brain and thyroid
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

3 makor plasma proteins responsible for transport?

A
  • TBG- thyroxine binding globulin
  • TBPA- thyroxine binding pre-albumin
  • albumin
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Thyroid fxn tests?

A
  • TSH
  • T4 - total serum level
  • T3 - total serum level
  • Free T4 index - calcultaion of Free T4 (FTI)
  • T3 resin uptake (used to calc. FTI)
  • thyroglobulin AB (Tg-Ab)
  • thyroid peroxidase AB (TPO-Ab)
  • TSH receptor ab (Anti-TSHR)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the best assessment of thyroid fxn?

A
  • TSH
  • assuming steady state conditions and absence of pituitary or hypothalamic disease
  • 3rd generation assay is the most sensitive
  • direct measurements of serum thyroid hormone levels still impt in some pts
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Thyroid ab tests?

A
  • TPO-Ab and Tg-Ab (high concentrations are seen in nearly all pts with Hashimotos thyroiditis)
  • TSH receptor stim. AB seen in graves
  • TSH receptor blocking Ab seen in atrophic Hashimoto’s thyroiditis and sometimes graves
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

mechanism of TSH?

A
  • secreted by the pituitary: responds to low levels of thyroid hormones, and responds to TRH (comes from hypothalamus)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

TSH testing is used for what?

A
  • dx a thyroid disorder in a person with sxs
  • screen newborns for an underactive thyroid
  • monitor thyroid replacement therapy in people with hypothyroidism
  • dx and monitor female infertility problems
  • help evaluate fxn of pituitary gland
  • screen adults for thyroid disorders as recommended by American thyroid association
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

interpretation of TSH normals>

A
  • differ b/t adults, newborns and cord

- will differ from lab to lab

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What happens to TSH as you age?

A
  • age related shift towards higher TSH concentrations in older pts
  • values will vary depending on lab
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

When will you see an elevated TSH?

A
  • hypothyroidism
  • thyroiditis
  • thyroid agenesis (newborns)
  • pituitary tumor
  • other severe and chronic illnesses
  • drug effects: iodine, ad thyroxine (T4)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

When will you see a low TSH?

A
  • hyperthyroidism
  • damage to pituitary gland that prevents it from making TSH (secondary hypothyroidism)
  • hypothalamus insufficiency (tertiary hyperthyroidism)
  • taking too much thyroid med for tx of underactive thyroid gland
  • drugs: excess T4 therapy, glucocorticoids, L -drops
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Importance of T4 (thyroxine)

A
  • prominent thyroid hormone (>90%)
  • nearly all of it is transported bound to proteins: TBG, albumin, transthyretin (TBPA)
  • only free (unbound) T4 is metabolically active
  • total T4 measures bound and free hormone
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Total T4 reliable test except for what interfering factors? - this measure both bound and free T4

A
  • decreased by PTU, NSAIDs, androgens, lithium, phenytoin, amidarone, salicylates, corticosteroids, and rifampin
  • increased by estrogens, heroin, amphetamines, OCP, pregnancy ( due to increased circulating protein)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

When will you see increased Total T4 levels?

A
  • hyperthyroidism
  • acute thyroiditis
  • conditions causing increased TBG (thyroid binding globulin)
  • pregnancy
  • meds: estrogens, heroin,, amphetamines, OCPs
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

When will you see decreased total T4 levels?

A
  • hypothyroid states
  • pituitary insufficiency
  • hypothalamic failure
  • protein malnutrition/depletion
  • iodine insufficiency
  • numerous other non-thyroid illnesses (CRF, cushings, cirrhosis, advanced cancer)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Why will altered levels of TBG change the value of the total T4?

A
  • direct measurement of thyroxine binding globulin (TBG) can be done and will explain the abnorm. value
  • excess TBG or low levels of TBG are found in some families as a hereditary trait. It causes no problem other than falsely elevating or lowering the total T4 level
  • these people are frequently misdx as being hyperthyroid or hypothyroid but they don’t have a thyroid problem and they don’t need any tx
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What does the free T4 index measure?

A

indirectly measures unbound T4

  • correction of misleading results of total T4 caused by conditions that alter the TBG
  • calculated product of the T3 resin uptake and serum T4
  • T3 resin uptake measures unoccupied binding sites on TBG, it isn’t a measure of T3
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is a more accurate test to measure Free T4?

A
  • Free T4
    fewer interfering factors:
    increased by heparin, ASA, and propranolol
    decreased by: furosemide, phenytoins
  • various wats to test free T4 but none of them directly measures unbound T4
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Indication for measuring free T4?

A
  • along with TSH, to dx hypo/hyperthyroidism
  • monitoring response to therapy along with TSH
  • gives a quicker result to response to tehrapy with replacent thyroxine than TSH
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Triiodothyronine (Total T3)

A
  • accounts for less than 10% of total thyroid hormone, large proporton formed by peripheral T4 to T3 conversion (liver)
  • 70% protein bound
  • less accurate test
  • interpretation: increased in hyperthyroidism, increased during pregnancy and by OCPs, and estrogens

decreased by androgens, phenytoin, propranolol, high dose salicylates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How do you calculate Free T4 using T3 resin uptake test?

A
  • incubate pt’s serum w/ radiolabeled T3 tracer
  • then add an insoluble resin that traps remaining unbound radiolabeled T3
  • the value reported is the % tracer bound to the resin
  • the number of free binding sites is determined by both binding protein levels and endogenous hormone production
  • thyroid hormone binding ratio (THBI) = pts T3 resin/normal pool resin
  • T3 resin uptake measures unoccupied binding site on TBG, it isn’t a measure of T3
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

T3 resin uptake: in hyperthyroidism would be?

A
  • high T4, high T3 resin uptake or THBI, high free index T4
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

TBG excess would have what T3 resin and T4 levels?

A
  • high T4
  • low T3 resin uptake or THBI
  • normal free index T4
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Hypothyroidism levels of T3 resin and T4?

A
  • low T4, low T3 resin uptake and low free index T4
29
Q

TBG deficiency levels of T3 resin and T4?

A
  • low T4, high T3 resin, normal free index of T4
30
Q

What is the Thyroid binding globulin?

A
  • most of thyroid hormones in blood are attached to protein called TBG
  • if there is an excess or deficiency of this protein it alters the T4 or T3 measurement but doesn’t affect the action of the hormone
  • if the pt appears to have normal thyroid fxn but an unexplained high or low T4 or T3 it may be due to an increase or decrease of TBG
  • direct measure can be doen and will explain abnormal value
  • excess or low TBG are found in some families as hereditary trait, it causes no problem except falsely elevateing or lowering T4 level
  • these pts are frequently misdx as being hyperthyroid or hypothyroid but have not problem
31
Q

TBG levels

A
  • major thyroid hormone transport protein
  • when TBG is elevate, T3 and T4 are elevated
  • affects the measurement of total T4/T3
32
Q

TBG levels are increased by?

A
  • pregnancy
  • infectious hepatitis
  • estrogens (OC, tamoxifen)
33
Q

TBG levels are decreased by?

A
  • protein losing conditions
  • malnutrition
  • major stress (steroids included)
  • androgens (testosterone)
  • drugs: phenytoin, propanolol
  • menopause
34
Q

What does the Free Thyroxine index (FTI or T7) measure?

A
  • evaluates thyroid fxn in pts with protein abnormalities (low albumin, low or high TBG)
  • calculated value, corrects for changes in protein binding, more closely approximates true hormone level
35
Q

Most common thyroid autoantibodies?

A
  • antithyroid peroxidase (TPO Ab)
  • antithyroglobulin (TgAb)
  • these abs work against thyroid peroxidase, an enzyme that plays a part in T4 to T3 conversion and synthesis process
  • causes chronic inflammation and destruction resulting in chronic thyroiditis
  • initially produces a mild hyperthyroidism: eventually leads to hypothyroid condition
36
Q

Indications for testing for thyroid autoabs?

A
  • hyperthyroid conditions: Hashimotos thyroiditis (if in hyperthyroid state), Graves disease
  • hypothyroid conditions: Hashimoto’s thyroiditis, myxedema
37
Q

Interpretation of thyroid autoantibodies?

A
  • nomral healthy people produce abs especially elderly women

- normal titers:

38
Q

TSHR antibodies?

A
  • immunoglobulins that stimulate or inhibit thyroid hormone release
  • autoimmune process and this can cross the placenta: neonatal hyperthyroidism (especially in neonate whose mother has Graves)
39
Q

Testing results of TSHR - stim ab

A
  • graves disease (sensitivity 90%)
  • TSHR stim Ab decline in graves tx with antihyperthyroid meds
  • TSHR stim ab will initially rise after radioiodine tx and then gradually drop although sometimes they may persist for years
  • TSHR stim. Ab will completely go away after a thyroidectomy
    • used to monitor level of disease and monitor progress of meds
  • TSHR blocking ab some pts with hashimoto’s thyroiditis have these - leads to hypothyroidism
40
Q

What is thyroglobulin?

A
  • protein precursor of thyroid hormones

- levels are low or undetectable with normal thyroid function

41
Q

When would thyroglobuin levels be elevated?

A
  • thyroiditis
  • graves disease
  • thyroid cancer
42
Q

When is thyroglobulin used as a tumor marker of thyroid tissue?

A
  • effectiveness of cancer tx
  • residual tissue post-op
  • metastasis
43
Q

When are TSH and free T4 tests done?

A
  • initial labs to establish hypothyroidism or hyperthyroidism, also used to monitor therapy
44
Q

WHen do you do a FTI (free thyroixine index)??

A
  • this can help determine if true elevatiin or depression of T4 or T3
45
Q

What does a TBG (thyroxine binding globulin) measure?

A
  • amount of binding proteins
46
Q

When would you test anti Tg and anti TPO?

A
  • when you are looking for AI diseases such as Hashimotos or graves
47
Q

When would you do a a TSH stim Ab/ TSH-blocking Ab test?

A
  • in graves disease and hashimotos
48
Q

What is a thyroglobulin test used for?

A

tumor marker

49
Q

When are thyroid nodules brought to attention?

A
  • when noted by pt
  • found by provider on PE
  • incidentalomas - found during other radiologic procedure (carotid US, neck CT)
50
Q

Who presents with thyroid cancer the most?

A
  • present in 4-6.5% of nodules
  • there is increased prevalence in children, adults 60 yo
  • people who have had head or neck irradiation, people with a family hx of thyroid cancer
51
Q

Steps to dx thyroid nodules?

A
  • first obtaina throrough history and PE
  • next measure TSH: if low usually indicates overtt hyperthyroidism
  • if high: more suspicious for cancer
  • next step: Thyroid US - to confirm presence of nodularity, assess sonographic features of nodule, assess for add. nodules and lymphadenopathy, assess for nodules for suspicious findings
52
Q

Indications for ultrasound?

A
  • US good at diff. cystic from solid nodules but won’t be able to tell if nodlue benign or malignant, can aid in determining which nodule to bx
  • allows accurate measurement of nodule;s size and can determine if a nodule is getting smaller or is growing larger
  • aids in performing thyroid FNA bx by improving accuracy if nodule can’t be felt easily on exam
53
Q

What US characteristics suggest a benign nodule?

A
  • nice sharp edges around nodule
  • fluid filled (Cystic) - not live tissue
  • multiple nodules (multi-nodular goiter)
  • no blood supply - not live tissue
54
Q

When should a FNA bx be done?

A
  • most accurate method for evaluating thyroid nodules and selecting pts for surgery
  • FNA bx of nodules >1-1.5 cm w/ suspicious findings on US
  • if there are any RFs nodules =/>0.5 cm are bx
  • pts without RFs nodules
55
Q

What levels of TSH are an indication that a FNA bx is needed?

A
  • when serum TSH is normal or elevated
56
Q

What should be done if TSH is low?

A
  • this can indicate that there is overt or subclinical hyperthyroidism
  • possibility that the nodule is hyperfunctioning, radioactive thyroid scan needs to be done next
  • don’t do a FNA, not as suspect
57
Q

Using a radionuclide thyroid scan?

A
  • uses either a radioactive or iodine tracer and special scanner to measure how much tracer is being absorbed:
  • iodine: shouldnt be done on pregnant women because it can cause fetal complications
  • technetium-99m (isotope uptake scan)
  • some cancers will look hot or warm on technetium scans but cold on iodine scans so it is usually better to do on iodine scans
58
Q

Process of radinuclide thyroid scan?

A
  • painless procedure
  • takes about 30 minutes
  • exposes pt to little or no radiation
  • somewhat costly
59
Q

Why would you do a radionuclide thyroid scan?

A
  • to determine functional status of a thyroid nodule
  • measure size of goiter prior to tx
  • follow up thyroid cancer pts after surgery
  • ID nodules and determining if hot or cold
  • locating thyroid tissue outside of neck, ex: base of tongue or in chest
  • used to select nodules for FNA
60
Q

How do you interpret a radionuclide thyroid scan?

A
  • gland may concentrate iodine normally but will be unable to convert the iodine to thyroid hormone so iodine tracer preferred
  • hot nodule: rapid uptake of iodine or isotope, less likely to be malignant
  • cold nodule: little or no uptake of iodine or isotope: more likely to be malignant
61
Q

Results of a radionuclide thyroid scan?

A
  • 95% of solitary thyroid nodules are benign
62
Q

What should you consider before doing a thyroid scan?

A
  • if pregnant or breastfeeding
  • hx of allergies: iodine, shellfish, bee venom
  • meds: thyroid hormones, antithyroid meds, meds that contain iodine: cough syrup, multivitamins, and amiodarone
63
Q

What will hot and cold nodules look like on a scan?

A
  • hot: darker than rest of thyroid

- cold: can’t see nodule, empty space

64
Q

What is favored a single nodule or multi-nodular thyroid?

A
  • multi-nodular is good finding
65
Q

What is a fine needle aspiration (FNA)?

A
  • non-surgical differentiation of malignant and benign nodules
  • cost effective, and safe
  • results are classified as:
    benign, follicular lesion of undetermined significance, follicular neoplasm, suspicious for malignancy, malignant, non-dx
66
Q

Determining if nodular is benign or malignant with FNA?

A
  • benign: consist of follicular epithelium with variable amount of colloid
  • malignant: can determine type: papillary, follicular variant of papillary, medullary, anaplastic, thyroid lymphoma, metastases to thyroid,
  • follicular CA and hurtle cell CA can’t be dx clearly by FNA bx (have to go in surgically)
67
Q

Suspicious findings from FNA

A
  • 10% of FNAs
  • not clearly benign nor malignant
  • 25% are found to be malignant when undergoing thyroid surgery
  • end up being follicular or hurthle cell cancers
  • surgery is recommended for suspcious aspiration
68
Q

Non-dx findings from FNA?

A
  • cytologically inadequate
  • repeat FNA under US guidance
  • consider core-needle bx
  • if still non-dx surgical excision needs to be considered
69
Q

How is thyroid function best assessed?

A
  • by measuring serum TSH, assuming steady state conditions and absence of pituitary or hypothalamic disease

Endocrinology (22 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions