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26 Cards in this Set
- Front
- Back
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nl tsh levels
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0.05-50mIU/L
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most of circulating t3 is from where
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liver
other major production is kidney can be made in cells, including pit |
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enzyme that peripherally converts t4 to t3
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Type 1 3',5' monodeiodinase, enzyme is labile and affected by very young/old and acute illness
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enzymes that pit uses to convert t4 to t3
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Type II monodeiodinase, enzyme is stable
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which test is most sensitive for detecting alterations in thyroid function
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TSH (first to change and last to resolve)
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in central hypothyroidism, what does the TSH look like
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usu nl, maybe sl high
but know it was hypothyroidism when you treat with T4, TSH becomes undetected |
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what do you do if you get a total T4 or T3 within central 75%
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conclude nothing, no additional testing
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what do you do if you get a T4 or T3 outside of the central 75%
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time to evaluate TBG
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hyperthyroid: T4 and T3RU
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T4 up
T3RU up |
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hypothyroid
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T4 down
T3RU down |
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increased TBG
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T4 up
T3RU down |
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decreased TBG
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T4 down
T3RU up |
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gold standard for detection of free T4
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equilibrium dialysis
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limitations of fT4
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acute illness and pregnancy - where TBG change - can alter conclusions
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where see antiTPO ab
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graves and hashimoto's
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stimulatory TSHr ab found
blocking TSHr ab found |
in graves - stimulatory
in atrophic thyroiditis - blocking |
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TSI test
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detects whether ab to TSHr are stimulating,blocking or nonactive (essentially detecting cAMP production)
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in hyperthyroidism, what changes first, second and third
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TSH suppressed first
then T3 goes up then T4 goes up free goes up before total |
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with recovery from hyperthyroidism, how enzymes change
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With recovery, T4 normalizes first, then T3,
TSH last (may take months); |
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first test to change in hypothyroidism
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TSH
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what are the results in hypothyroidism
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high TSH Low free, total T4, low T3RU
T3 can be nl in 30-40%; T3 stays up in failing thyroid |
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in acute illness what will thyroid tests look like
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decreased T3 (reduced peripheral conversion) but all others are nl
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in high TBG states what will thyroid tests look like
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increased T4 (and T3), reduced T3RU, nl TSH, nl fT4
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in low TBG states what will thyroid tests look like
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low T4 (and T3), increased T3RU, nl TSH, nl freeT4
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causes of high TBG
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drugs: phenothiazines, opiates
estrogen (OCPs, pregnancy) active liver dz (leaks out) |
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causes of low TBG
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cirrhosis
nephrotic syndrome congenital deficiency in |
