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Boards.CP.Chemistry > Thyroid > Flashcards

Thyroid Flashcards

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1
Q

What is elevated in most hyperthyroid patients and decreased in hypothyroidism?

*What is found in <5% of Hyperthyroid patients?

A

Total T4 (Thyroxine)

  • <5% of Hyperthyroid patients:
  • Normal T4 but elevated T3 (“T3 Toxicosis”)
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2
Q

Since T4 and T3 are highly bound, fluctuations in serum proteins somewhat limit their values, What are the two main binding proteins?

A
  • Prealbumin (Transthyretin)

- Thyroid Binding Globulin (TBG)

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3
Q

Measurements of what, correlates well with clinical thyroid status?

A

Free T4 (FT4) and Free T3 (FT3)

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4
Q

What is Reverse T3 (rT3)?

*It is elevated in what?

A

rT3 is a metabolic product of T4 (most of which is metabollized to T3)

*rT3 is elevated in Euthryoid Sick Syndrome

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5
Q

Thyroid Function Test Patterns - Hyperthyroidism:

  • TSH
  • T3
  • T4 (Total)
  • T4 (Free)
  • rT3
A

Hyperthyroidism:

  • TSH - Low
  • T3 - High
  • T4 (Total) - High
  • T4 (Free) - High
  • rT3 - wnl
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6
Q

Thyroid Function Test Patterns - Hypothyroidism:

  • TSH
  • T3
  • T4 (Total)
  • T4 (Free)
  • rT3
A

Hypothyroidism:

  • TSH - High
  • T3 - Low
  • T4 (Total) - Low
  • T4 (Free) - Low
  • rT3 - wnl/Low
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7
Q

Thyroid Function Test Patterns - Euthyroid Sick Syndrome:

  • TSH
  • T3
  • T4 (Total)
  • T4 (Free)
  • rT3
A

Euthyroid Sick Syndrome:

  • TSH - wnl
  • T3 - Low
  • T4 (Total) - wnl/Low
  • T4 (Free) - wnl/Low
  • rT3 - High
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8
Q

Thyroid Function Test Patterns - Excess TBG:

  • TSH
  • T3
  • T4 (Total)
  • T4 (Free)
  • rT3
A

Thyroid Function Test Patterns - Excess TBG:

  • TSH - wnl
  • T3 - High
  • T4 (Total) - High
  • T4 (Free) - wnl
  • rT3 - wnl
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9
Q

What is the clinical scenario for testing Thyroid Releasing Hormone (TRH)?

A

Evaluation of Hypothyroidism

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10
Q

An exaggerated secretion of Thyroid Stimulating Hormone (TSH) in response to Thyroid Releasing Hormone (TRH), suggests what?

A

Primary Hypothyroidism

-Hypothyroidism d/t Intrinsic Thyroid Hypofunction

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11
Q

An inappropriate TSH response to TRH stimulation suggests what?

A

Hypopituitarism

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12
Q

What is the best first line test for diagnosing hypo- and hyperthyroidism?

A

Thyroid Stimulating Hormone

TSH; Thyrotropin

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13
Q

TSH levels:

  • Hypothyroidism
  • Hyperthyroidism
A

TSH levels:

  • Hypothyroidism - High
  • Hyperthyroidism - Low
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14
Q

In which clinical scenarios may TSH not be the best screening test? (3)

A
  • Hypothalamic dysfunction
  • Pituitary dysfunction
  • Neonatal Screening (fT4)
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15
Q

What is the next step if FT4 is normal despite a low TSH?

A

Measure free T3 (FT3)

-Assess for T3 throtoxicosis

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16
Q

What is the most common cause of Hyperthyroidism?

A

Graves disease

17
Q

Graves Disease is characterized by the presence of what? (1+)
-Which other antibodies may also be seen? (2)

A

Thyroid Stimulating Immunoglobulin (TSI)/Long Acting Thyroid Stimulating (LATS) Antibodies

  • Antimicrosomal Abs (60%)
  • Antithyroglobulin Abs (30%
18
Q

What is the most common cause of Hypothyroidism?

A

Hashimoto Thyroiditis

19
Q

Hashimoto Thyroiditis is characterized by the presence of what 2 antibodies?

A
  • Antitissue Peroxidase Abs (>90%)

- Antithyroglobulin Abs (>90%)

20
Q

What is Neonatal Hypothyroidism most often caused by?

A

Thyroid Dysgenesis

21
Q

Neonatal Hypothyroidism:

  • Complications (if untreated)
  • MC Test for evaluation
A
  • Mental/Growth Retardation

- TSH assay alone

22
Q

What is the effect of Exogenous Estrogens on Thyroid function?

A

Increases TBG

  • Increase Total Thyroxine (T3/T4)
  • Free Thyroxine and TSH are WNL
23
Q

What medication inhibits the release of Thyroxine from the Thyroid gland, resulting in Hypothyroidism?

A

Lithium

24
Q

Amiodarone effect on Thyroid Function:

  • Developed countries (iodine rich)
  • Underdeveloped countries (iodine poor)
A

Amiodarone effect on Thyroid Function:

  • Developed countries (iodine rich) - Hypothyroidism
  • Underdeveloped countries (iodine poor) - Hyperthyroidism

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