Flashcards in week 9- endo 2 Deck (80)
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• TSH testing:
o measures pit stim of thyroid
o ↑: thyroid doesn’t make enough T4 (1st hypo)
o ↓: 1) hyperthyroid, 2) abn pit doesn’t make TSH (2nd hypo)
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• Thyroid hormone state:
o free=available for uptake
o bound=circulating storage pool
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• T4 tests:
o Total T4: bound + free. ~99% on TBG (doesn’t enter tissues)
o fT4/fTI (index): Free; measured direct or calc as fTI= free/bound. helps tell if abn T4 is dt abn TBG (pg, viral hepatitis, cirrhosis, breast CA)
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• Triiodothyronine (T3)
o ↑: hyperthyroid (st ↓TSH, ↑T3 & T4 mb normal)
o Hypothyroid: T3 mb normal (w ↑TSH, ↓T4)
o PG and OCPs: ↑ both total T4 & T3
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• N TSH, N fT4, NT3:
o Euthyroid
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• N TSH, N/↑ fT4, N/↑T3:
o Euthyroid hyperthyroxinemia
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• N TSH, N/↓ fT4, N/↓ T3:
o Euthyroid hypothyroxinemia
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• ↑ TSH, N fT4, N T3:
o Subclinical hypothyroid
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• ↑TSH, ↓fT4, N/↓T3:
o Primary hypothyroid
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• ↓TSH, N fT4, N T3:
o Sunbclinical hyperthyroid
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• ↓TSH, ↑/N fT4, ↑T3:
o Hyperthyroid
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• T3-Resin uptake:
o serum inc w radiolabeled T3 tracer
o insoluble resin added to trap remaining unbound radio-T3
o Result: % tracer bound to resin (inverse of # free binding sites for T3)
o Distinguish TBG excess and def from hyper/hypo-thyroid
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• ↑ tT4, ↑T3RU, ↑FTI:
o Hyperthyroid
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• ↑ tT4, ↓T3RU, N FTI:
o TBG excess
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• ↓ tT4, ↓T3RU, ↓ FTI:
o Hypothyroid
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• ↓ tT4, ↑T3RU, N FTI:
o TBG def
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• Serum Reverse T3:
o rT3 = biologically inactive, dt deiodination of T4 (diff enzyme), mainly in liver
o ↓ T3 & ↑ rT3: mb ssx hypothyroid → ↑ protein synthesis and O2 consumption by all cells
o ↑ rT3: mb chronic dz, Wilson’s syndrome
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• Anti-thyroid antibodies (ATA):
o a-TG: (+) in Hashimoto’s
o a-thyroperoxidase (a-TPO): catalyzes iodination of tyrosine; ↑ in Hashimoto’s
o TSH receptor (TRAb)
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• TRH test:
o serum TSH measured after inj w TRH to determine if thyroid problems dt ↓ TRH (3rd hypothyroid, rare)
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• Thyroglobin (Tg):
o Monitor w thyroid CA w thyroid glands removed
o =protein produced by normal thyroid cells and thyroid CA cells
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• Radioactive Iodine Uptake (RAIU):
o swallow sm amt radioactive iodine
o ↑: thyroid gland is overactive
o ↓: underactive
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• Thyroid Scan:
o may show diffusely high or low intake or discrete (nodular) areas of high (Hot nodule) or low (cold nodule) intake
o gets a “picture” of the gland
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• Ultrasound:
o used to determine if a nodule is solid or cystic
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• Goiters
o = enlarged thyroid gland; diffuse or nodular
o Mb seen in normal, hypo/hyperthyroid
o Geographical differences in incidence dt I def
o Etio: I def (endemic goiter), ↑TSH, Grave’s, Pg
o Many of no clinical significance but full assessment needed
o Ssx: often asx. Early: pressure/lump in throat, choking sensation, dyspnea, dysphagia
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• Goiter staging:
o Normal: ~20g in size
o 0: not visible; non-palpable
o 1: possibly visible; mb palpable, ↓40 g
o 2: visible; easily palpable, ~40 g
o 3: visible, palpable, > 40g
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• Goiter work-up:
o Labs: TFTs, ATAs
o neck x-rays, thyroid scan, US w needle bx = gold standard for dx
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• Euthyroid (Simple) Goiter:
o dt ↓thyroid fxn w/o clinical dz.
o Etio: Endemic, pg, menopause, hormone effects, I
o goitrogens interfere w I uptake (Brassicas, soy, peanuts, millet, strawberries, peaches, sweet potato, etc)
o drugs (amino-salicylic acid, sulfonylureas, lithium)
o Labs: ↑TSH, ↓T4 in hypothyroid
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• Thyroid nodules:
o Usu benign, scan to r/o malig
o Labs: TSH, FT4, ATA titers, serum Ca
o Thyroid US, fine-needle aspiration bx
o Thyroid scan: “hot” nodules in hyperfxn, “cold” in non-fxn, “warm” = nodule w normal fxn
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• Hypothyroidism, causes:
o F > M, tends to be familial; gland mb small and fibrotic, or goiter
o Causes: inherited enzymatic defects, AI, RAI exposure, anti-thyroid drugs, dietary goitrogens, thyroidectomy, inflam, granuloma, neoplasms, congenital aplasia, pituitary failure
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