Thyroid Labs (lec 2) Flashcards
TSH regulated by what?
Negative feedback of T3
T3/4 circulate how?
99% protein-bound
(U) to TBG
Thyroid hormones are the only substances in the body that contain what?
iodine
Primary thyroid disorders affect what?
thyroid gland
2° thyroid disorders affect what?
Ant pituitary
3° thyroid disorders affect what?
hypothalamus
Hyperthyroidism due to?
Overproduction of thyroid hormone
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
Hypothyroid due to?
Fxnl inactivity of thyroid gland
Causes of Hyperthyroid?
Graves Toxic Nodular Goiter Thyroiditis Postpartum thyroid Excess iodine High TSH Ectopic thyroid tissue
Hyperthyroid sxs? (7)
Nervous Sweating Heat intolerant Fatigue/Weak Irreg menstruation Palpitation Frequent BMs
Hyperthyroid signs? (10)
Stare Lid lag Ptosis Goiter Warm/Moist skin Weight loss Tachycard Systolic murmur A fib Tremor
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
Hypothyroid sxs? (6)
Fatigue/weak Cold intolerance Arthralgia/Myalagia Constipation HA Depression
Hypothyroid signs? (8)
Puffy face Periorbital edema Dry skin Hair loss (esp lat eyebrow) Weight gain Hoarseness Slow speech Menorrhagia/Galactorrhea
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
