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Old 03-28-2013
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Thyroid Thyroid suppression test

can any one tell m the each and everything and every detail abt thyroid suppression test ?
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Old 03-29-2013
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Ok, lets do this, one step at a time! It is my hope, that after reading this, not only will u be able to teach this to someone else, but u will remember this for life! pls let me know if i left anything out, or if there are other things u'd like to add, or if anything here might be incorrect, or not clear.

ok, so u got a patient that comes in. and something is FISHY with this patients thyroid. u don't know exactly what's up, so u decide to run some TESTS!!!

First of all, u know hypo vs hyper, (too much vs too little thyroid hormone). the basics. ok, now lets take it from there. oh, one more points we might as well address here..radioactive iodide uptake. if its increased ---> that indicates a HYPERFUNCTIONING thryoid gland. if decreased ----> indicates a HYPOFUNCTIONING thryoid gland.

ok, that's the basics out the way. lets move on!!!

The KEY PLAYER here is TSH! (remember this) TSH stimulates the thyroid gland, right? Of course. so REMEMBER ONE THING RIGHT NOW ----> when we talk about Thryoid Suppression or Stimulation tests, we are actually refering to the STIMULATION or SUPPRESSION of TSH!!!

so lets discuss each separately. First we'll discuss how we suppress TSH, then we'll discuss how we stimulate TSH

Suppression of TSH

We suppress TSH by giving the patient Thyroid Hormone. So how does thyroid hormone exactly suppress TSH you ask? glad u asked! there are 2 ways it does this. First, thryroid hormone inhibits the secretion of TRH from the hypothalamus (negative feedback yo!). Second, thryoid hormone actually decreases the sensitivity of the TRH receptor on the pituitary gland!!! (pretty nifty, right). NET RESULT -----> Decreased TSH Secretion (TSH = suppressed)

Stimulation of TSH

This is pretty much self explanatory. we stimulate TSH by giving the patient TRH. Not sure if i need to explain this, because it makes sense as is. (TSH = stimulated)

Okay, okay, okay. ur probably asking yourself: "well thanks for the info reggie, but what does all this information mean???? how do i use this info to help diagnose my patient!!!!!" don't fret! now with the basic understanding we have, we can now get to the JUICY STUFF!!! Lets look at each test separately, so we can see where they might be used clinically!

The Thyroid Stimluation Test

lets say u have a patient with hypErthyroidism (of thryoid origin). so u now have increased thyroid hormone. what does this thyroid hormone do? well, for one, it will decrease the sensitivity of the TRH receptors on the pituitary (read above if you didn't get this). so lets say we give this patient TRH. guess what, this TRH is not gonna do much, because the TRH receptors have decreased sensitivity!!!! u might get some TSH secreted, but not much at all!!!

But lets now take a different patient who has HypOthyroidism (from thryoid origin)...u know thyroid levels are low, and u also know that TRH receptors on the pituitary are just waiting to get stimulated!!! so in this situation, we give TRH, and BOOOOOOM!!! TSH get SECRETED!!!!!! and that results in HIGH TSH!!!

The Thyroid Suppresion Test

In this test, u give Thyroid Hormone to SUPPRESS TSH (see above). If you Suppress TSH, that means TSH levels decrease. And decreased TSH means that Thryoid doesn't get stimlated. So what does this mean?? Well, lets say you have a NORMAL patient. Obviously, this normal patient you have now supprsed his thyroid gland, and this is seen as a DECREASED UPTAKE OF RADIOACTIVE IODINE UPDTAKE!!!

but what if this patient is NOT normal? what if he has... a Thyroid Hormone Secreting Adenoma??? OMG, what now!!! well, quite simply, it means that despite ur valiant attempts to suppress his thyroid gland, u won't be able to, because that adenoma will function autonomously, and you will NOT see decreased uptake of radioactive iodine.

Last edited by ReggieMiller; 03-29-2013 at 12:22 PM.
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Endocrine-, Pathology-, Physiology-

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