premonition
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 Nope. I looked up google and it probably hovers somewhere around Sick Euthyroid Syndrome...
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| chemamr
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yeah, itīs the same than the Sick euthyroid syndrome.
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| gpsbrar
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yep it is sometimes due to systemic illnesses like pneumonia and septicemia or after minor surgery or also with malnutrition. It is characterized by decrease in 5'-monoiodinase activity in the peripheral tissues like liver and kidneys. It (low t3 synd) is considered to be protective adaptation to decreased catabolic processes during the illness.
I guess this helps.
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| graceluv
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Thanks!
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| ssrpk
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very well gpsbrar! good explanation!
why is the TSH normal in these instances ? 
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| cyra
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Isn't TSH also low/low normal in the sick euthyroid syndrome?...i thought the general trend in this sydrome was for "everything to be low".....Looking forward to the explaination ssrpk!..
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| KEROCHI
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TSH is the most sensitive test in thyroid disease, if the TSH is normal, then the patient is euthyroid.
Total T4 & T3 do not always reflect actual thyroid function. For example, increased TBG levels are seen in pregnancy & the use of oral contraceptives. This will increase total T4 but free or active T4 level is normal.
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| ssrpk
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well TSH will remain normal because free T4 remains normal, realize that most of the circulating free T3 comes about by the perioheral conversion of cirulating T4 via 5'-deiodinase and so is the negative feedback effect which is mediated mainly by free T4 rather than T3! Low T3 syndrome is characterized by decrease in the actrivity of 5'-deiodinase (as gpsbrar mentioned), therefore it's the circulating free T3 levels that will decrease without any significant change in the levels of T4.
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| ssrpk
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one more thing!
circulating activity of thyroid hormones is mediated by free T3 rather than T4 , while feedback effect is mediated by free T4, it's kind of parellel effects of the two, so don't mix them up!
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| an
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r u sure about that?...coz there is a type II deiodinase in the pituitary that mediates conversion of T4 to T3...and this enz is not selenium dependent...whereas the type I deiodinase found in periphery requires selenium...and it is this deficiency found in acute illness that results in low T3 in periphery...
so within pituitary T3 levels would be ok....
i am not sure about this point...any corrections would be welcome...
Edited by an on 09/13/05 - 06:53 AM
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| p53
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Yes, within pituitary T3 levels would be OK (but they reflect peripheral T4 content, because pituitary T3 is derived mostly from the peripheral T4 conversion. Peripheral T4 content is normal), so TSH would be OK. In periphery T3 level would be low. You are talking the same thing, ssrpk and an!
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