Thyroid Gland: Lab Flashcards

1
Q

Difficulties in Interpreting Thyroid Function Tests



- as seen in hospitalized px with acute psychiatric illness
- due to medications

A

presence of abN° binding proteins (congenital or drug-induced)

alterations in hormone metabolism:

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2
Q

Hormone Measurements

A

• TRH
• TSH
• free T4
• free T3

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3
Q

Hormone Measurements
_
- assays for this is not clinically useful
- difficult to develop specific antibody for an immunoassay

A

TRH measurement

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4
Q

Hormone Measurements

- can identity virtually all instances of hyper- and hypothyroidism, except when:
• Damage to hypothalamus or pituitary gland
• Thyroid hormone resistance
• Interference with normal functioning of HPT axis due to medication

A

TSH measurement

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5
Q

Hormone Measurements
• TSH measurement
- can identity virtually all instances of hyper- and hypothyroidism, except when:

A

• Damage to hypothalamus or pituitary gland
• Thyroid hormone resistance
• Interference with normal functioning of HPT axis due to medication

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6
Q

TSH measurement

reference range:

A

0.5 - 5.0 microunits per milliliter (µU/mL)

Microinternational Unit per Liter

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7
Q

TSH measurement
- immunoassay

A

• first-generation assay
• second-generation assay
• third-generation assay
• fourth-generation assay

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8
Q

• RIA
• not sensitive enough

A

first-generation assay

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9
Q

• TSH measurement
- first-generation assay

A

• RIA
• not sensitive enough

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10
Q

• improved sensitivity (0.1 - 0.2 mU/L)
• monoclonal or polyclonal antibodies

A

second-generation assay

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11
Q

• TSH measurement
- second-generation assay

A

•improved sensitivity (0.1 - 0.2 mU/L - milliunits/ liter)
• monoclonal or polyclonal antibodies

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12
Q

• TSH measurement

• refinements in immunometric method
• sensi: 0.005 mU/L
• now common in use

A
  • third-generation assay
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13
Q

• TSH measurement
- third-generation assay
• refinements in
• sensi:
• now common in use

A

immunometric method

0.005 mU/L

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14
Q

TSH measurement

• recently developed
• sensi: 0.0004 mU/L
• not widely available

A
  • fourth-generation assay
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15
Q

TSH measurement
- fourth-generation assay
• recently developed
• sensi:
• not widely available

A

0.0004 mU/L

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16
Q
  • biologically active fraction
A

Free Thyroxine (FT4)

17
Q

Free Thyroxine (FT4)

traditional reference method
• not affected by changes in binding protein concentration

A

Equilibrium Dialysis

18
Q

Free Thyroxine (FT4)

4 methods

A
  • Symmetrical Dialysis
  • Ultrafiltration
  • Tandem Mass Spectrometry
  • Immunoassay: more common
19
Q
  • immunoassay after the hormone is separated from the carrier protein
  • often used along with TSH measurement
A

Thyroxine (total T4)

  • 5.5 - 1.25 mg/dL
20
Q

• T3
- immunoassay
-
- generally not useful in evaluating hypothyroidism
• decreased in px with severe hypothyroidism

A

60 to 160 mg/dL (0.9 to 2.46 nmol/L)

21
Q


- little clinical significance
- high in healthy newborn or px with NTI, hyperthyroidism and those taking amiodarone and propanolol

A

rT3

22
Q
  • up to about 30 ng/mL (45 pmol/L)
  • thyroid mass, thyroid injury, and TSH receptor stimulation
  • increased in Graves’ disease, thyroiditis, and nodular goiter
  • tumor marker for thyroid malignancy
A

Thyroglobulin

23
Q

Thyroglobulin
- up to about 30 ng/mL (45 pmol/L)

increased in_____’ disease, thyroiditis, and nodular goiter

A

Graves

24
Q


- immunoassay
- 13 - 39 mg/dL (150 - 360 nmol/L)
- inherited TBG abnormalities
• complete/partial deficiencies, decreased affinity for T4 or T3, and TBG excess

A

TBG

25
Q

• TBG

Method

Reference range

A
  • immunoassay
  • 13 - 39 mg/dL (150 - 360 nmol/L)
26
Q


- classical method of adjusting a total Ta measurement for alterations in binding protein
- Estimate of the amount of TBG sites unsaturated by T4

A

T2 uptake (T3-UP) test

27
Q
  • should be measured in all patients before Tg analysis
  • in iodide-deficient areas, serum TgAb measurement can be used to detect autoimmune thyroid disease in patients with a goiter and to monitor iodide therapy in endemic areas
A
28
Q

Measurements

- previously known as TSI

A

TSH receptor Ab (TRAbs)

29
Q
  • Graves’ disease
    •_______ of cases
A

TRAb + in 85%

30
Q

TRAb + in 85%

A

• TSH receptor Ab (TRAbs)

  • Graves’ disease
31
Q

Urinary lodine

A
  • to assess the dietary iodine intake
  • for iodine deficiency disorders
  • accurate estimate of dietary iodine intake
32
Q

Urinary lodine
= normal
= mild deficiency
= moderate deficiency
L = severe deficiency

A
  • > 100 mg/L
  • 50-99 g/L.
  • 20-49 pg/L
  • <20 mg/
33
Q

Assay used for TSH

A

Immunoassay