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Chemical Pathology > Thryoid Function Tests > Flashcards

Thryoid Function Tests Flashcards

1
Q

Name 9 indications for TFTs

A

• Symptomatic patient, features of thyroid disorder, elderly and menopausal woman with nonspecific symptoms,
• family history
• taking thyroxine

Patients at risk of developing thyroid disease:
• diabetes: type 1 annually, type 2 at diagnosis
• autoimmune disease (annual)
• treated hyperthyroidism (annual)
• downs and turner’s syndrome (annual)
• post neck irradiation (annual)
• lithium or amiodarone (before treat and 6 monthly)

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2
Q

Name 3 types thyroid hormone

A

• Thyroxine T4 (produced by thyroid)
• tri-iodo thyronine T3 (biologically active,formed in liver kidneys muscle from T4 )
• reverse T3 (rt3)

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3
Q

Which proteins binds thyroid hormones (3)

A

. Thyroxine binding globulin TBG = major binding protein
• transthyretin / thyroxine binding prealbumin
• albumin

99,8% bound. 0,05% free T4, 0,2% free T3

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4
Q

How does amiodarone affect thyroid function
(4)

A

• Decrease thyroid hormone secretion
. Induce hyperthyroidism
. Impaired T3 and T4 conversion
• modified thyroid hormone action

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5
Q

How does lithium affect thyroid function (3)

A

• Decrease thyroid hormone secretion
• induce hyperthyroidism
• decrease in thyroidal synthesis

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6
Q

How does iodine affect thyroid function (2)

A

• Decrease thyroid hormone secretion
• induce hyperthyroidism

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7
Q

Name 10 causes low tsh

A

High free T4:
• overt hyperthyroidism

Normal T4
• subclinical hyperthyroidism !
• T3 hyperthyroidism (T3 toxicosis - do thyroid isotope scan)!
• non-thyroidal illness!
• treated hyperthyroid patients first 6 months
• ophthalmic Graves’ disease
• pregnancy first 20 weeks
• treatment with dopaminergic drugs or high dose glucocorticoids

Low T4
• non thyroidal illness
• hypopituitarism uncommon

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8
Q

Name 5 causes normal tsh with thyroid derangements

A

High free T4
• tsh oma (rare)
• assay interference
• thyroid hormone resistance (uncommon)

Low T4
• northyroïdal illness
• hypopituitarism (un common)

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9
Q

Name 7 causes high tsh

A

High free T4
• tsh Oma (rare)
• assay interference
• thyroid hormone resistance (uncommon)

Normal T4
• subclinical hypothyroidism
• recovery from nonthyroidal illness

Low T4
. Overt hypothyroid
• recovery from nonthyroidal illness

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10
Q

Name 2 signs hyperthyroid

A

• Exophthalmos
• goiter

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11
Q

Name 4 signs hypOthyroid

A

• Hair dry, coarse, sparse
• lateral eyebrows thin
• periobital edema
• puffy dull face with dry skin

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12
Q

When is tsh only ideal as a first line test

A

• Monitor on thyroxine
• screen at risk patients that are asymptomatic

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13
Q

When is tsh only not ideal as a first line test (5)

A

• Symptomatic patient on first presentation
• optimising treatment
• screening and monitorin in pregnancy
• diagnose and monitor hypopituitarism
• diagnose tsh Oma and thyroid hormone resistance (rane)

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14
Q

Approach to hypothyroidism with tsh 4,5 -10 and FT 4 normal (5)

A

• Exclude recovery from illness and drug causes
• repeat at 3 months to exclude transient rise in tsh (subclinical hypothyroid )
-if still no increase, do not treat with T4 unless Goitre, pregnancy
-If > 10, treat.
• request anti-tpo antibodies → positive → treat

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15
Q

Approach to hypothyroidism with tsh > 10 and FT 4 normal (4)

A

• Confirm subclinical hypothyroidism by repeat in 3 months.
• start on T4 if still >10
• retest after 8 weeks of treatment and change as needed
• when stable, annual check with tsh

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16
Q

Approach to hypothyroidism with tsh > 10 and FT 4 <9

A

Overt hypothyroid = treat with T4

17
Q

Name 10 causes hypothyroid

A

Congenital
• thyroid aplasia
• dyshormogenesis

Acquired primary
• Iatrogenic
• inflammatory:
- autoimmune: hashimoto, atrophic thyroiditis
- transient: viral thyroiditis, postpartum thyroiditis

Acquired secondary
• hypopituitarism
• hypothalamic dysfunction
. Iodine deficiency

18
Q

Name 7 causes hyperthyroid

A

. Inflammatory
- Graves’ disease (autoimmune, tsh receptor stimulating antibodies)
-Thyroïdites (sudden release T4) eg de Quervain thyroiditis (usually TRANSIENT with infection, resolve when remove infection)
• toxic multinodular goitre, solitary toxic nodule
• iodine induced (chronic high iodine intake or amiodarone which contains iodine)
• tsh Oma
• factitions (hypothyroid treatment)
. Trophoblastic (hcg identical to tsh so can stimulate thyroid)

19
Q

Treatment and monitoring hyperthyroid?

A

• Radioiodine
• carbimazole
• thyroïdectomy

Can only measure tsh again after 4-6 months

20
Q

Approach to tsh 0,01 - 0,2 and normal FT4 and T3? (2)

A

• Rule out northyroidal illness, dopamine agonists, high dose glucocorticoids
• Repeat at 6 months to see if it’s subclinical hypothyroidism → still low → treat

21
Q

Approach to tsh < 0,01 and normal FT4 and T3? (2)

A

• Rule out northyroïdal illness, dopamine agonists, high dose glucocorticoids
• repeat in 1-2 months to see if sub clinical hyperthyroid → still low → refer

22
Q

Approach to tsh < 0,01 and raised FT4 and or T3?

A

Overt hyperthyroidism
Refer for treatment

23
Q

Name 8 lab test changes in hyperthyroid

A

• Hyperglycaemia /impaired glucose tolerance
• hypocholesterol
. Abnormal LFTs
• hyperca
• increase shbg
- Decrease sodium Na
- increase prolactin
- increase ck

24
Q

Name 4 cases in which TFTs may be unreliable

A

• Northyroidal illness/sick euthyroid syndrome (usually low T3, low tsh 2x more likely due to NTI than hyperthyroid and usually > 0,01, )
• illness recovery ( usually rise tsh, more likely than hypothyroid )
• neonate (initial surge tsh, then marked decline )
•Pregnancy

25
Q

Name 4 other tests that can be done for thyroid disease

A

• Thyroid cancer: follicular carcinoma (thyroglobulin tumour marker)
• TRH test: secondary hyperthyroid due to tsh Oma or thyroid hormone resistance
• anti thyroid peroxidase antibodies
• tsh receptor antibodies TRABs

26
Q

Name 4 causes of abnormal TFT in euthyroidism

A

• Abnormal TBG
• genetic variants albumin and pre-albumin: familial dysalbuminaemic hyperthyroxinaemia
• assay interference: patients with endogenous antibodies that interfere with the assays

27
Q

T3 vs T4

A

T3: active
T4: inactive, transformed to T3 (used to measure)

28
Q

Name 7 causes high T4 (hyperthyroid)

A

Low TSH

  • overt hyperthyroïd

Normal TSH: uncommon

  • TSHoma
  • assay interference
  • thyroid hormone resistance

High TSH: uncommon
- same as above

29
Q

Name 5 causes normal T4 with abnormal TSH

A

Low TSH

  • subclinical hyperthyroidism
  • T3 hyperthyroidism
  • Nonthyroïdal illness!

Normal TSH = euthyroid

High TSH

  • subclinical hypothyroidism
  • recovery from non thyroidal illness
30
Q

Name 6 causes low T4 (hypothyroid)

A

Low TSH

  • non thyroïdal illness
  • hypopituitarism (uncommon)

Normal TSH

  • non thyroïdal illness
  • hypopituitarism

High TSH

  • overt hypothyroid
  • Recovery from non thyroïdal illness

Chemical Pathology (23 decks)

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