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Discussion Starter · #1 ·
A 2 year old boy brought by his mother for a well child visit. His height and weight are both on the 50th centile. He has history of hypothyroidism and thyroditis in the family. His mother insist that he should be tested for thyroid function. Which of the following serum levels would provide most definitive evidence of normal thyroid function?

A- Free T4
B- Iodine/Iodide
C- TSH
D- Total T4
E- Total T3
 

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A 2 year old boy brought by his mother for a well child visit. His height and weight are both on the 50th centile. He has history of hypothyroidism and thyroditis in the family. His mother insist that he should be tested for thyroid function. Which of the following serum levels would provide most definitive evidence of normal thyroid function?

A- Free T4
B- Iodine/Iodide
C- TSH
D- Total T4
E- Total T3
A- Free T4
 

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Discussion Starter · #6 ·
TSH is the most sensitive test

Thyroid Stimulating Hormone (TSH) is a pituitary gland hormone, which is sent from the brain-center or what might be referred to as the "central command post" that monitors and regulates the amount of thyroid hormone released from the thyroid gland. It increases when the thyroid needs to produce more hormone and it decreases when it needs to produce less but in a non-diseased thyroid gland, these fluctuations stay within normal values. When hypothyroidism (under-active thyroid) or hyperthyroidism (overactive thyroid) occurs, TSH will begin to fall outside of the normal values range.
Because of how finely-tuned TSH keeps the thyroid gland, it will change its level in the body with even to most subtle changes in thyroid function. If for example the thyroid becomes less able to provide adequate hormone in the body due to damage in the gland from a disease process affecting it, TSH will increase in level before thyroid hormones decrease in levels. It will continue to do so even when the thyroid becomes unable to supply normal amounts. During its attempt to keep the thyroid going at normal speed, the TSH hormone will be what first becomes abnormal on blood lab tests. This makes TSH the single best and earliest indicator of developing thyroid hormone imbalance that is available.

The T3 and T4 thyroid hormone levels can be tested as the "total" levels or the "free" levels. Many thyroid specialists and endocrinologists believe that the free levels are the better blood tests. This is due to the fact that patients, who take cortisol steroid treatments, estrogen therapy or have certain medical conditions such as liver disease or pregnancy, can experience a change in the level of a thyroid protein called TBG (thyroxine-binding globulin). Much of the T3 is bound in the blood by this protein (total level) with the free, unbound T3 that is left over, being more active in regulating bodily metabolism.
Certain types of scenarios can change the free-circulating level of remaining T3 hormone in the body that is available including cases of thyroid disease. Depending on each particular case, this can result in Total T3 testing normal, while the Free T3 will test outside of normal values, better detecting thyroid hormone imbalances in some cases.
 
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