Endocrinology > Thyroid Labs and Imaging > Flashcards

Thyroid Labs and Imaging Flashcards

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1
Q

Thyroid Hormones

3

A

Thyroxine(T4)
Triiodothyronine(T3)
Calcitonin

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2
Q

Thyroxine T4:

Is present how and must be converted to what?

A

greatest amount of thyroid hormone

T4 must be converted to the “active” hormone T3

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3
Q

Whats the most biologically active thyroid hormone?

A

Triiodothyronine(T3)

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4
Q

Where does calcitonin come from?

A

Produced in the parafollicular cells (aka C- cells) of the thyroid

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5
Q

Calcitonin is involved in regulating blood levels of calcium and phosphate by?
2

A
  1. Inhibits osteoclast activity

2. Decrease resorption of calcium in the kidneys

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6
Q

Describe thyroid hormones and their solubility in plasma?

How much of T3 and T4 is unbound?

What kind of T3 and T4 can penetrate cellular membranes and exert biologic activity by interacting w/ nuclear receptors?

Where is T4 converted to T3? 5

Three major plasma proteins responsible for transport?

A

Thyroid hormones are poorly soluble in plasma

0.03% of T4 and 0.3% of T3 unbound (not much)

Only free T3 and T4

Especially in the

  1. liver,
  2. gut,
  3. skeletal muscle,
  4. brain and the
  5. thyroid

Three major plasma proteins responsible for transport:

  1. TBG- Thyroxine Binding Globulin
  2. TBPA-Thyroxine binding pre-albumin
  3. Albumin
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7
Q

Thyroid Function Tests 5

What are the three antibody tests?

A
  1. Thyroid-Stimulating Hormone (TSH)
  2. Thyroxine (T4)—Total Serum level
  3. Triiodothyronine (T3)—Total Serum level
  4. Free T4 Index—calculation of Free T4 (FTI)
  5. T3 Resin Uptake (Used to calculate FTI)
  6. Thyroglobulin Antibody (Tg-Ab)
  7. Thyroid Peroxidase Antibody (TPO-Ab)
  8. Thyroid stimulating hormone receptor antibody (Anti-TSHR)
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8
Q

The best assessment of thyroid function is what?

Assuming what?

A

TSH

Assuming steady state conditions and the absence of pituitary or hypothalamic disease

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9
Q

What is the most sensitive assay for the TSH test?

A

It is important to know what generation of assay is being used to run the TSH test—the third generation assay is the MOST sensitive

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10
Q

Antibodies (Ab):
TPO-Ab and Tg-Ab high concentrations are seen in what disease?

TSH receptor stimulating Ab seen in what disease?

TSH receptor blocking Ab seen in what? 2

A

nearly all patient’s with Hashimoto’s thyroiditis

Grave’s disease

atrophic Hashimoto’s thyroiditis and sometimes in Grave’s

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11
Q

What is TSH secreted by?

What does it respond to?
2

Where does TRH come from?

A

Secreted by pituitary

  1. Responds to low levels of thyroid hormones
  2. Responds to Thyrotropin Releasing Hormone (TRH)

The hypothalamus!

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12
Q

TSH testing is used to?

6

A
  1. diagnose a thyroid disorder in a person with symptoms
  2. screen newborns for an underactive thyroid
  3. monitor thyroid replacement therapy in people with hypothyroidism
  4. diagnose and monitor female infertility problems
  5. help evaluate the function of the pituitary gland (occasionally)
  6. Screen adults for thyroid disorders as recommended by some organizations, such as the American Thyroid Association
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13
Q

What are normal TSH levels in:
Adults?
Newborns?
Cord?

A

0.5 – 5.9 microunits/mL
3-18 microunits/mL
3-12 microunits/mL

Dont really need to memorize these

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14
Q

Age-related shift towards what kind of TSH concentrations in older patients?

A

higher

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15
Q

Elevated TSH is seen in the following conditions?

6

A
  1. Hypothyroidism
  2. Thyroiditis
  3. Thyroid agenesis (newborns.. screened by law)
  4. Pituitary tumor
  5. Other severe and chronic illnesses
  6. Drug effects: Iodine, Thyroxine
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16
Q

Low TSH in these conditions?

5

A
  1. Hyperthyroidism
  2. Damage to the pituitary gland that prevents it from making TSH (Secondary hypothyroidism)
  3. Hypothalamus insufficiency (Tertiary hyperthyroidism)
  4. Taking too much thyroid medicine for treatment of an underactive thyroid gland
  5. Drugs: excess T4 therapy, glucocorticoids, L-dopa
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17
Q

How is nearly all Thyroxine (T4) transported?

3

A

bound to proteins:

  1. Thyroxine binding globulin (TBG)
  2. Albumin
  3. Transthyretin (thyroxine-binding prealbumin–TBPA)
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18
Q

What form of T4 is metabollically active?

What does total T4 measure?

A

Only free (unbound) T4 is metabolically active

Total T4 measures bound and free hormone

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19
Q

Total T4 Very reliable test but many potentially interfering factors such as:
Decreased by? 9
Increased by? 5

A

Decreased by:

  1. PTU,
  2. NSAIDs,
  3. androgens,
  4. lithium,
  5. phenytoin,
  6. amiodarone,
  7. salicylates,
  8. corticosteroids,
  9. rifampin

Increased by:

  1. estrogens,
  2. heroin,
  3. amphetamines,
  4. OCP,
  5. pregnancy (due to increased circulating protein)
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20
Q

Critical values for total Thyroxine T4:
Adults?
Newborns?

A

Adult: less than 2 or over 20

Newborn:
less than 7

Probably dont need to memorize

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21
Q

Interpreting Total T4 Levels:
Increased? 5
Decreased? 6

A

Increased:

  1. Hyperthyroidism
  2. Acute thyroiditis
  3. Conditions causing increased TBG (thyroid binding globulin)
  4. Pregnancy
  5. Meds listed on previous slide

Decreased:

  1. Hypothyroid states
  2. Pituitary insufficiency
  3. Hypothalamic failure
  4. Protein malnutrition/depletion
  5. Iodine insufficiency
  6. Numerous other non-thyroid illnesses (CRF, Cushings, cirrhosis, advanced cancer)
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22
Q

Altered levels of what will change the value of the Total T4?

A

TBG

People with excess or low levels of TBG are frequently misdiagnosed as being hyperthyroid or hypothyroid, but they have no thyroid problem and need no treatment

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23
Q

What does the free T4 index measure?

It is a calculated product of what?

A

Indirectly Measures Unbound T4

Calculated product of the T3 resin uptake and serum T4

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24
Q

T3 resin uptake measures what?

A

unoccupied binding sites on TBG, it’s not a measure of T3!

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25
Indications for measuring Free T4? | 3
1. Along with TSH, diagnose hypo/hyperthyroidism 2. Monitoring response to therapy along with TSH 3. Gives a quicker result to response to therapy with replacement thyroxine then TSH
26
Free T4 is increased by what? 3 Decreased by what? 2
Fewer interfering factors: - Increased by: 1. heparin, 2. ASA, 3. propranolol - Decreased by: 1. furosemide, 2. phenytoins
27
A large proportion of Triiodothyronine (Total T3) is formed by what? How much is protein bound? How accurate is this test?
Large proportion formed by peripheral T4 to T3 conversion (liver) 70% protein-bound Less accurate test than Free T4
28
Total T3 is increased in what? 3 What is it decreased by? 4
1. Increased in Hyperthyroidism 2. Increased during pregnancy and other conditions that cause an increase in proteins 3. Increased by: estrogen, Oral contraceptives, Decreased by: 1. androgens, 2. phenytoin, 3. propranolol, 4. high-dose salicylates.
29
Calculating Free T4 Index Using the T3 Resin uptake test: The value reported is what? The number of free binding sites is determined by? 2
The value reported is the percent tracer bound to the resin The number of free binding sites is determined by both 1. binding protein levels 2. endogenous hormone production
30
THBI is what? The T3 resin uptake was designed to distinguish what? T3 resin uptake measures what?
patient’s T3 resin/normal pool T3 resin TBG excess and deficiency from hyper- and hypo- thyroidism unoccupied binding sites on TBG, it's not a measure of T3!
31
Results of T3 Resin Uptake: 3 for each 1. Hyperthyroidism: 2. TBG excess: 3. Hypothyroidism: 4. TBG defiency:
1. High T4, high T3 resin uptake or THBI, high free index T4 2. High T4, low T3 resin uptake or THBI, normal free index T4 3. Low T4, low T3 resin uptake or THBI, low free index T4 4. Low T4, high T3 resin uptake or THBI, normal free index T4
32
Most of the thyroid hormones in the blood are attached to a protein called what? If there is an excess or deficiency of this protein it alters what? If a patient appears to have normal thyroid function, but an unexplained high or low T4, or T3 what may it be due to?
thyroid binding globulin (TBG) the T4 or T3 measurement but does not affect the action of the hormone. it may be due to an increase or decrease of TBG
33
Thyroid Binding Globulin (TBG) is what kind of protein? When its elevated what else is elevated?
Major thyroid hormone transport protein When TBG is elevated, T3 and T4 are elevated Affects measurement of total T4/T3
34
Thyroid Binding Globulin (TBG) is increased by what? 3 Decreased by what? 6
Increased by: 1. Pregnancy 2. Infectious hepatitis 3. Estrogens (including OC, Tamoxifen) Decreased by 1. Protein-losing conditions 2. Malnutrition 3. Major stress (including steroids) 4. Androgens (Testosterone) 5. Drugs: Phenytoin, Propranolol 6. Menopause
35
Free Thyroxine Index (FTI or T7) evaluates what? What does it correct for?
Evaluates thyroid function in patients with protein abnormalities (low albumin, low or high TBG) Corrects for changes in protein-binding
36
Most common thyroid autoantibodies? | 2
``` Antithyroid Peroxidase (TPO Ab) Antithyroglobulin (TgAb) ```
37
These antibodies work against what, an enzyme that plays a part in the T4-to-T3 conversion and synthesis process ? What does this cause? 2
thyroid peroxidase 1. Causes chronic inflammation and destruction resulting in chronic thyroiditis 2. Initially produces a mild hyperthyroidism Eventually leads to hypothyroid condition
38
Indications for testing thyroid autoantibodies? 2
1. Hyperthyroid conditions – Hashimoto’s thryoiditis (if in hyperthyroid state), Grave’s Disease 2. Hypothyroid conditions – Hashimoto’s thyroiditis, Myxedema
39
Thyroid Autoantibodies lab interpretation? 2 Other conditions affecting test results? 3
Interpretation 1. Normal healthy people produce antibodies – especially elderly women 2. Normal titers: less than 1:100 1. Rheumatic autoimmune diseases (including RA) 2. Pernicious anemia 3. Thyroid carcinoma
40
Immunoglobulins that stimulate or inhibit thyroid hormone release are what? What should we know in pregnant women?
Thyroid Stimulating Hormone (TSHR) antibodies Cross placenta – neonatal hyperthyroidism (especially neonate whose mother has Graves)
41
TSHR-stimulating Ab is a positive test for what?(sensitivity 90%)
Graves disease
42
what is a Protein precursor of thyroid hormones? Levels are low or undetectable with normal thyroid function. Can be elevated with?3 Used as a tumor marker and used for what?3
Thyroglobulin (Tg) Can be elevated with: 1. Thyroiditis 2. Grave’s Disease 3. Thyroid Cancer Used as tumor marker of thyroid tissue: 1. Effectiveness of cancer treatment 2. Residual tissue post-op 3. Metastasis
43
Initial labs to establish hypothyroidism or hyperthyroidism, also used to monitor therapy? 2 What can help determine if true elevation or depression or T4 or T3? Measures amount of binding proteins?
TSH, Free T4 FTI (free thyroxine index) TBG (thyroxine binding globulin)
44
Used for looking for autoimmune diseases such as Hashimotos and Grave’s disease? 2 Grave’s disease and Hashimoto’s lab? 2 Used as a tumor marker? 1
Anti Tg and Anti TPO (antithyroglobulin Ab and antithyroid peroxidase Ab) TSH-stimulating Ab/TSH-blocking Ab Thyroglobulin
45
Increased prevalence in of thyroid cancer? | 4
1. Children 2. Adults less than 30YO and those greater than 60 YO 3. People who have had head or neck irradiation 4. People with a family history of thyroid cancer
46
First step when finding a thyroid nodules on a PE? Low when? High when? Whats the next step and why do we do this? 4
First step – measure TSH If it is low usually indicates probable overt hyperthyroidism If it is high more suspicious for cancer NEXT step Thyroid US to: 1. Confirm presence of nodularity 2. Assess sonographic features of the nodule(s) 3. Assess for additional nodules/lymphadenopathy 4. Assess for nodule(s) for suspicious findings
47
Thyroid US indications? | 3
1. Good at differentiating cystic from solid nodules but it will not tell if a nodule is benign or malignant but can aid in determining which nodule(s) to biopsy 2. Allows accurate measurement of a nodule's size and can determine if a nodule is getting smaller or is growing larger 3. Aids in performing thyroid fine needle aspiration (FNA) biopsy by improving accuracy if the nodule cannot be felt easily on examination 1. cystic from solid nodule (which ones to biopsy) 2. If its growing or not based on size 3. Aids with FNA
48
Ultrasound characteristics which suggest a benign nodule? | 4
1. Nice sharp edges around nodule 2. Fluid filled (cystic) – not live tissue 3. Multiple nodules (multi-nodular goiter) 4. No blood supply – not live tissue
49
What is the Most accurate method for evaluating thyroid nodules and selecting patients for surgery?
FNA biopsy
50
Thyroid Nodule Management If serum TSH is normal or elevated then what do we do? If the sreum TSH is low what can it indicate? 2 What should be done next?
fine needle aspiration (FNA) biopsy is indicated 1. Overt or subclinical hyperthyroidism 2. Possibility that the nodule is hyperfunctioning Radioactive thyroid scan needs to be done next
51
What uses either a radioactive or iodine tracer and special camera (Computerized Rectilinear Thyroid Scanner) to measure how much tracer is being absorbed? Who is it contraindicated in? What will a lot of cancers look like on iodine scans?
Radionuclide Thyroid Scan Should not be done on pregnant women – iodine can cause fetal complications. cold
52
Radionuclide Thyroid Scan: Radiation exposure risk?
little or none
53
Why do a radionuclide thyroid scan? | 6
1. Determine functional status of a thyroid nodule 2. Measure size of goiter prior to treatment 3. Follow-up thyroid cancer patients after surgery 4. Identifying nodules and determining if they are "hot" or "cold" 5. Locating thyroid tissue outside the neck, i.e. base of the tongue or in the chest 6. Used to select nodules for FNA
54
What does a hot nodule indicate? 2 What does a cold nodule indicate? 2
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
55
Things to consider before a thyroid scan | 3
Pregnant or breastfeeding History of allergies Medications
56
Things to consider before a thyroid scan: Allergies to look out for? 3
Iodine Shellfish Bee venom
57
Things to consider before a thyroid scan: Medications to look out for? 3
1. Thyroid hormones 2. Antithyroid meds 3. Meds that contain iodine Cough syrups, multivitamins, amiodarone
58
Non-surgical differentiation of malignant and benign nodules that is cost effective, safe? Results are classified how? 6
Fine Needle Aspiration - FNA 1. Benign 2. Follicular lesion or atypia of undetermined significance 3. Follicular neoplasm 4. Suspicious for malignancy 5. Malignant 6. Non-diagnostic
59
Fine Needle Aspiration (FNA) that consists of follicular epithelium with variable amount of colloid is what kind of nodule?
Benign
60
FNA can deteremine the type of malignant nodule. What kinds are there? 6 Which ones cannot be diagnosed by FNA? 2
1. Papillary 2. Follicular variant of papillary 3. Medullary 4. Anaplastic 5. Thyroid lymphoma 6. Metastases to thyroid 1. Follicular CA and 2. Hurthle cell CA cannot be diagnosed clearly by FNA biopsy!!
61
Suspicious FNAs – (10% of FNA’s) are what?
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 suspicious aspiration
62
Non-diagnostic FNAs are what? What should we do after these results? 3
Cytologically inadadequate Repeat the FNA under US guidance Consider core-needle biopsy If still non-diagnostic surgical excision needs to be considered
Endocrinology
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