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I'm trying to get a grasp on TSH levels and hyper/hypo thyroidism. Does TSH sensitive indicate one or the other?

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

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What is TSH?

What does it stimulate?

Is TSH high or low in primary hypothyroidism?

Is TSH high or low in primary hyperthyroidism?

TSH is thyroid stimulating hormone, produced by the pituitary to signal the thyroid to produce more thyroxine. Normal values should be between 0.4 and 4.0 mIU/L (although some sources say as high as 5.5). A high TSH value indicates hypothyroidism, but some pts with much higher values may be asymptomatic, while others may be symptomatic with values as low as 5.0 - 5.5. Triiodothyronine (T3) and thyroxine (T4) tests should also be pulled to get a more complete picture, but bear in mind that these values can be affected by a number of medications.

Yes but what does TSH "sensitivity" mean?

Are you talking about the TSH sensitive lab test? It detects very low TSH levels and can indicate hypothyroidism before symptoms become advanced.

http://www.medscape.com/viewarticle/452667_5

TSH is thyroid stimulating hormone, produced by the pituitary to signal the thyroid to produce more thyroxine. Normal values should be between 0.4 and 4.0 mIU/L (although some sources say as high as 5.5). A high TSH value indicates hypothyroidism, but some pts with much higher values may be asymptomatic, while others may be symptomatic with values as low as 5.0 - 5.5. Triiodothyronine (T3) and thyroxine (T4) tests should also be pulled to get a more complete picture, but bear in mind that these values can be affected by a number of medications.

Such as Lithium?

It's also important to note that hyper/hypothyroidism can appear like either mania/depression.

Yes but what does TSH "sensitivity" mean?

In healthy patient:

TSH attaches to the thyroid gland >> The thyroid gland makes T3 and T4 >> Higher levels of T3 & T4 tell the hypothalamus to stop making so much TRH >> less TRH >> less TSH >> less T3 and T4.

Elevated TSH with low T3 and T4 is indicative of primary hypothyroidism. I believe that in this form of hypothyroidism, the thyroid is where the pathology is. The TSH is probably high because it's trying to keep t3 or t4 levels up but the thyroid is diseased so it never responds hence low t3 and t4.

Decreased TSH with high T3 and T4 is indicative of primary hyperthyroidism. In this form of hyperthyroidism (called Graves) you have antibodies that keep stimulating the thyroid to make t3 and t4.

The TSH sensitivity test may be referring to when they give (TRH ... I believe) and they watch to see what happens to TSH levels.

TSH levels remain low/unchanged the Dx most likely will be primary hyperthyroidism.

TSH levels respond a lot then you have yourself a Dx of primary hypothyroidism.

AN members please correct me as I'm just 1 week shy from graduation and still putting puzzles together, and don't wanna give wrong info.

Specializes in Pedi.
In healthy patient:

TSH attaches to the thyroid gland >> The thyroid gland makes T3 and T4 >> Higher levels of T3 & T4 tell the hypothalamus to stop making so much TRH >> less TRH >> less TSH >> less T3 and T4.

Elevated TSH with low T3 and T4 is indicative of primary hypothyroidism. I believe that in this form of hypothyroidism, the thyroid is where the pathology is. The TSH is probably high because it's trying to keep t3 or t4 levels up but the thyroid is diseased so it never responds hence low t3 and t4.

Decreased TSH with high T3 and T4 is indicative of primary hyperthyroidism. In this form of hyperthyroidism (called Graves) you have antibodies that keep stimulating the thyroid to make t3 and t4.

The TSH sensitivity test may be referring to when they give (TRH ... I believe) and they watch to see what happens to TSH levels.

TSH levels remain low/unchanged the Dx most likely will be primary hyperthyroidism.

TSH levels respond a lot then you have yourself a Dx of primary hypothyroidism.

AN members please correct me as I'm just 1 week shy from graduation and still putting puzzles together, and don't wanna give wrong info.

You are correct, in primary hypothyroidism the problem is with the thyroid. The TSH levels are high because the brain is trying to get the thyroid to produce more T3 and T4 in response to low circulating levels.

Primary care doctors (and other non-Endocrinologists) often rely on the TSH alone which they shouldn't. My Endocrinologist always shakes his head when he sees that other MDs have checked my TSH without checking T3, T4 and free T4. This is because I have pituitary dysfunction so if I have an issue with my thyroid, it's much more likely to be central than it is to be a primary thyroid problem. In central hypothyroidism, you would see a low TSH with low circulating thyroid hormones. The thyroid isn't producing the hormones because the brain isn't telling it to.

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