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When you order TSH you always order FREE -T4 which is a standard..
Noone order ONLY TSH...
and the TSH is teh most sensitive bc in Primary HYPO(Hashimotos ) you hav eincreased TSH , while in secondary you have decreased TSH,
Primary the problem is in teh gland, secondary the problem can be either hypopituirism or hypothalamic cause
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well i thought clinically....
thx
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Free T4 is the active one bound to ???
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it would not preced...it comes after.
first tsh then ft4
if u read the title of q....they have already assessed hypothyroid...how u do that is by tsh....no one is questioning that..
they are asking next step after that....to determine low tsh with low t4 or high t4
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Represents a calculated free T4 hormone concentration
It is calculated by multiplying the total serum T4 by the T4 BR.
The FT4 is low and high in hypo- and hyperthyroidism, respectively.
The measured total serum T4 ( and T3 ) reflects hormone that is both bound to thyroid binding globulin (TBG ) and hormone that is free ( metabolically active at the tissue level )
Changes in either the free hormone level ( hypo “ or hyperthyroidism ) or the concentration of TBG ( estrogen increases, androgens decrease TBG synthesis ) alter the total serum T4.
TBG alterations do not affect the free hormone level because is regulated by the normally functioning T4-TSH feedback mechanism.
The resin T3 uptake (RTU ) reflects the TBG concentration.
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u can't order it alone without other pituitary hormons
plasma TSH is usually within the reference range in secondary hypoth and cant be used alone to make the diagnosis.
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The serum TSH has a negative feedback relationship with circulating T4 and T3
It is single best test for diagnosing primary hypothyroidism ( increased TSH )
Hyperthyroidism ( decreased TSH
May be used as a radio nuclide scan of the thyroid to detect nodules or as an index of thyroid activity.
Since thyroid hormone represent tyrosine with iodides attached to it:
true hyper functioning of the gland (e.g., Graves™ disease ) increases the uptake of I 131
hypo functioning gland has a decreased uptake
The RTU and T4 Br are low in hypo and high in hyperthyroidism, respectively.
However, the RTU and T4Br are both increased when TBG is decreased ( less binding site, hence more is left over )
Decreased when TBG is increased ( more binding sites, hence less is left over )
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isn't resin test an obsolete test that used to calculate the FT4???
