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Medical Diagnostics > Thyroid Labs > Flashcards

Thyroid Labs Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the only organ that synthesizes T4?

A

Thyroid

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2
Q

Where does 80% of circulating T3 derive from?

A

T4

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3
Q

Only _____ T3 and T4 can enter cells

A

free (unbound)

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4
Q

What tests make up the thyroid panel?

A
  • TSH
  • Total T4
  • Total T3
  • Free T4
  • Free T3
  • Thyroxine binding globulin
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5
Q

What stimulates the thyroid to produce T4&T3?

A

TSH (Thyroid Stimulating Hormone)

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6
Q

What is the first test you should order for suspected thyroid disorder?

A

TSH

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7
Q

Where is TSH secreted from?

A

Anterior pituitary

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8
Q

What factors can cause an increased TSH?

A
  • Primary HYPOTHYROIDISM
  • Thyroiditis
  • Large doses of iodine
  • Severe and chronic illnesses
  • Pituitary TSH-secreting tumor
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9
Q

What factors can cause a decrease in TSH?

A
  • Secondary hypothyroidism (pituitary dysfunction)
  • HYPERTHYROIDISM
  • Pituitary hypofunction
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10
Q

What is total T4 a measure of?

A
  • Amount of T4 that is bound to protein and free
  • Direct measurement of T4 in the blood serum
  • Used to rule out hyper and hypothyroidism
  • Range = 4-12
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11
Q

What can cause an increased level of T4?

A
  • Primary HYPERTHYROIDISM (Grave’s disease, toxic thyroid adenoma)
  • Acute thyroiditis
  • Pregnancy
  • Thyroid cancer
  • Toxic multinodular goiter
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12
Q

What can cause a decrease in total T4 levels?

A
  • HYPOTHYROID state (cretinism, surgical ablation of the thyroid, Myxedema)
  • Pituitary insufficiency
  • Hypothalamic failure
  • Protein depleted states (nephrotic syndrome)
  • Renal failure, cirrhosis, cushing disease, surgery, advanced cancer)
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13
Q

T3 is more _____ than T4, but its effects are _____

A

Active, shorter

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14
Q

What percent of T3 is bound to proteins?

A

70%

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15
Q

What percent of thyroid hormone is T3?

A

7-10%

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16
Q

What some causes of an increased T3?

A
  • Primary Hyperthyroidism (Grave’s disease, toxic thyroid ademona)
  • Acute thyroiditis
  • Pregnancy
17
Q

What are some causes of a decreased T3?

A
  • Hypothyroidism
  • Hypothalamic failure
  • Protein malnutrition and other protein depleted states
  • Iodine insufficiency
  • Liver disease (this is where T4 gets converted to T3)
18
Q

What is free T4?

A

Amount of thyroxine that is unbound in the blood

  • Active and available to tissues (gets converted to T3)
  • *Controls metabolism**
19
Q

What is free T3?

A

Amount of triiodothyronine that is unbound in the blood

  • Active
  • Controls metabolism
20
Q

What is thyroxin-Binding globulin?

A

Carries T3 and T4 in the blood stream (this is the protein that T3 and T4 bind to)

21
Q

What directly impacts TOTAL T3 and T4 concentration but not FREE T3 and T4?

A

-Amount of TBG impacts total T3/T4 but not free T3/T4 because it is not bound to it

22
Q

When do we order thyroid testing?

A
  • Suspect patient to have hypothyroidism
  • Suspect patient to have hyperthyroidism
  • Abnormal thyroid exam
23
Q

Who do we screen?

A

If people are complaining of symptoms -> TSH

  • Normal TSH = no further testing
  • High TSH = free T4 to determine degree of hypothyroidism
  • Low TSH = free T4 and T3 to determine degree of hyperthyroidism
24
Q

When would you order both TSH and T4 right away?

A
  • If pituitary or hypothalamic disease is suspected (ie young woman who hasn’t gotten her first period yet)
  • If TSH comes back normal but there is high suspicion of hyper or hypothyroidism
25
Q

When should you NOT order TSH/T3/T4?

A

In acutely ill patients!!!

because it will be off

26
Q

What are symptoms of hypothyroidism?

A
  • Fatigue
  • Cold intolerance
  • Weight gain
  • Dry skin
  • Brittle nails
  • Hair loss
  • Constipation
  • Poor memory
27
Q

What are the values of TSH/T4/T3 in hypothyroidism?

A
  • Decreased T4/T3
  • Increased TSH
  • *Negative feedback loop**
28
Q

What are symptoms of hyperthyroidism?

A
  • Hyperactive, insomnia
  • Excessive sweating
  • Weight loss
  • Increased appetite
  • Tachycardia
  • Tremor
  • Exophthalmos (bugging eyes)
  • Anxiety
29
Q

What are the values of TSH/T4/T3 in hyperthyroidism?

A
  • Increased T4/T3

- Decreased TSH

30
Q

What 3 things can interfere with TSH levels?

A
  1. Biotin supplements
  2. Age (older = higher TSH)
  3. Weight (obese = higher TSH)

Medical Diagnostics (10 decks)

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