Thyroid Labs (lec 2) Flashcards by Wendy Pitts

TSH regulated by what?

Negative feedback of T3

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T3/4 circulate how?

99% protein-bound

(U) to TBG

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Thyroid hormones are the only substances in the body that contain what?

iodine

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Primary thyroid disorders affect what?

thyroid gland

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2° thyroid disorders affect what?

Ant pituitary

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3° thyroid disorders affect what?

hypothalamus

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Hyperthyroidism due to?

Overproduction of thyroid hormone

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Thyrotoxicosis is?

Clinical result of excess thyroid hormone,

not necessarily due to over prdxn -> could be leak of hormone from thyroid gland or ingestion of hormone

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Hypothyroid due to?

Fxnl inactivity of thyroid gland

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Causes of Hyperthyroid?

Graves
Toxic Nodular Goiter
Thyroiditis
Postpartum thyroid
Excess iodine
High TSH
Ectopic thyroid tissue

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Hyperthyroid sxs? (7)

Nervous
Sweating
Heat intolerant
Fatigue/Weak
Irreg menstruation
Palpitation
Frequent BMs

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Hyperthyroid signs? (10)

Stare
Lid lag
Ptosis
Goiter
Warm/Moist skin
Weight loss
Tachycard
Systolic murmur
A fib
Tremor

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Causes of Hypothyroidism:

Primary?

2°?

3°?

Primary (dz of gland):
Hashimoto (autoimm destr) *most common
Iodine deficiency in diet   *most C outside US
Latrogenic (surgery/radiation)
Postpartum

2°: Pituitary dz

3°: Hypothalamus dz

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Hypothyroid sxs? (6)

Fatigue/weak
Cold intolerance
Arthralgia/Myalagia
Constipation
HA
Depression

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Hypothyroid signs? (8)

Puffy face
Periorbital edema
Dry skin
Hair loss (esp lat eyebrow)
Weight gain
Hoarseness
Slow speech
Menorrhagia/Galactorrhea

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Best screening test for thyroid dysfxn?

Hyperthyroid levels?

Hypothyroid levels?

TSH (3rd generation)

Hyper < 0.10

Hypo > 7

Best test for Hypothyroid?

Best test for Hyperthyroid?

Plasma TSH

Free T4

Normal TSH excludes what conditions?

Hyper

Primary Hypo

Plasma T4 used to confirm?

1) Hypo in pts w/ high TSH

2) Hyper in pts w/ low TSH, also tells us severity

T4 assays measure?

total T4 (free and bound)

Thyroid Hormone-Binding Globulin (TBG) increased by what hormone?

Decreased by?

Estrogen

Androgens

Free T4 most helpful when?

pts w/ abnormal proteins

T3 Resin Uptake (T3RU) tells us?

If total T4 really indicates Hyper, Hypo or if issue is w/ TBG

T3RU inversely proportional to TBG

Relationship b/w Total T4 and T3RU:

If move in same direction?

If move in opposite direction?

Same direction = thyroid issue

Opp direction = TBG (binding) issue,
If this then run Free T4

T3-RIA (Free T3) used when?

signs/sxs of Hyper w/ normal TFT

Antithyroglobulin Antibodies (Anti-Tg Ab) occur when?

thyroglobulin acts as immune-stimulating antigen -> Ab's attack thyroglobulin -> inflamm/destruction of thyroid gland

Antithyroid Peroxidase Antibodies (Anti-TPO Ab) occur when?

Ab's made to microsomes from thyroid epithelial cells -> Microsomes act as antigens -> stim Ab prdxn -> Inflamm/Toxins to thyroid follicle

Thyroid-Stim Immunogloblulins (TSI) are?

IgG Ab against thyroid TSH receptors 90% of Grave's have these

Screening TSH: If normal? If high? If low?

Normal = no more tests High = Free T4, all Ab's Low = Free T4/3, Ab's

Radioactive Iodine Uptake (RaIU) tells us: Hyper w/ decreased uptake? Hyper w/ increased uptake?

early thyroiditis Grave's

Radionuclide Scan tells us?

Function of thyroid gland (size, hot/cold areas)

Thyroid US tells us?

Size of gland Nodule presence and composition Follow dz

Hyperthyroid tx? (3)

PTU/Methimazole (blocks I-) Lithium Iodide (blocks T4 release) β-block (block T4 to T3, helps sxs)

Asympt thyroid nodule w/ normal Labs and RaIU, next step?

Radionuclide Scan Cold nodules U don't take up iodine If cold then Fine Needle Aspiration

Hypothyroid tx?

T4 on empty stomach Check TSH in 6 wks: If TSH high -> need to ↑T4 If TSH low -> need to ↓T4

Risks of over-treating Hypo?

a fib | bone disease

Use of T4 to tx CA/Goiter?

T4 to ↓ TSH to very low levels