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TSH Blood Test: Useful or Useless?

Learn why thyroid-stimulating hormone (TSH) is a common test used to assess thyroid function, and what it means in the big picture.
TSH Blood Test: Useful or Useless?

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Thyroid conditions can be relatively straightforward to diagnose with the right tools. Indeed, by catching problems early on, people can have an action plan for keeping their thyroid healthy throughout their life. One of the best ways to assess thyroid function is with a thyroid blood test. By looking closely at various thyroid hormone levels in your body, a doctor can determine if your thyroid is functioning appropriately or not. Let’s talk about one of the most essential thyroid blood tests—TSH, and what it tells us about how to manage a thyroid condition like hypothyroidism.

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What is TSH?


TSH is short for thyroid-stimulating hormone. TSH is not made by the thyroid gland but is released by the pituitary gland in the brain. The pituitary releases TSH based on the feedback it receives from thyroid hormones circulating in your bloodstream. 


The thyroid gland itself produces and releases the thyroid hormones: thyroxine (T4) and triiodothyronine (T3). If these thyroid hormones are low, it signals the pituitary gland to release more TSH to stimulate the thyroid to make more hormones. Alternatively, if thyroid hormone levels are high, the pituitary will release less TSH, so the thyroid decreases production.

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How is TSH tested?


We measure TSH with a simple blood test. Typically, doctors and clinicians will order a blood test involving blood drawn from a vein in your arm. However, you can also order your own TSH test with an at-home thyroid test kit that only requires a finger stick instead of a venipuncture blood draw.


Once your blood sample is collected, a lab evaluates the amount of TSH in the sample. Normal parameters may vary based on the lab with which you work. Still, generally, most labs consider a TSH between 0.5 to 5.0 mIU/L within a normal range. 

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Why is TSH important?


Thyroid hormone production is based on a feedback system, where all hormones and related endocrine organs are important. To get a complete picture of how the thyroid functions, you need to understand what the pituitary is doing. The only way to assess pituitary functioning in this whole feedback loop is to assess thyroid-stimulating hormone (TSH).


If TSH is high, it indicates that the thyroid is underactive and may suggest a patient has hypothyroidism. On the contrary, if TSH is low, it may show that the thyroid is overactive and the patient has hyperthyroidism. However, these diagnoses cannot be made solely based on TSH levels.


Other markers necessary to evaluate thyroid function


Testing TSH alone is not sufficient enough to deliver the complete picture of how your thyroid is working. And sometimes, it is not useful, such as in people who have a pituitary disease or a history of pituitary radiation or surgery. 


Most thyroid specialists order additional tests like free T4 and free T3. These are hormones produced by the thyroid and converted into a useable form once released into the bloodstream. 


Additionally, some providers who are exceptionally proficient in thyroid care will order TPO antibodies. Antibodies are proteins in the body that serve to protect against infections and other invaders. Sometimes, antibodies can mistakenly attack your own tissues. 


TPO (thyroid peroxidase) is an enzyme in the thyroid gland that produces thyroid hormones. Part of the role of TPO is to covert iodide ions from food to a usable form for the production of T4 and T3. Suppose you do not have enough thyroid hormones in your bloodstream. In that case, an increase in TSH will also signal an additional production of TPO. 


If TPO antibodies are present in your bloodwork, it may indicate your immune system is attacking healthy tissues in your thyroid. Autoimmune destruction of the thyroid gland is one of the leading causes of hypothyroidism. This condition is called Hashimoto’s thyroiditis. Of course, the presence of TPO antibodies does not always mean that you have clinical hypothyroidism. Still, it does mean there is a constant attack on your thyroid gland, which may lead to thyroid problems in the future.


How TSH changes with treatment


People with clinical hypothyroidism typically need medication to increase their thyroid hormone levels to support the body’s needs. Thus, thyroid hormone replacement medications serve to mimic the body’s natural thyroid hormone so that they can raise thyroid hormone levels to signal the pituitary to stop releasing so much TSH. Indeed, most people with hypothyroidism should see an improvement in their TSH levels once they are on the correct dose of medication. 


People on medication after thyroid surgery or cancer treatment may require higher doses of medication to reach an optimal TSH level.


Sometimes, people have thyroid symptoms without an abnormal TSH reading. People who have a TSH on the upper end of normal with symptoms may be considered to have subclinical hypothyroidism. Those with subclinical hypothyroidism may still benefit from treatment even though TSH is within an acceptable range. Treatment should be personalized on a case-by-case basis with your thyroid doctor.


Even if you have subclinical hypothyroidism, you and your thyroid doctor will want to monitor your TSH to make sure it stays at an appropriate level. 


So, is TSH useless or useful? 


Testing TSH is necessary to provide a complete picture of how the thyroid gland is functioning. However, a TSH test should be used with other thyroid tests to give a comprehensive view of your thyroid function. For comprehensive thyroid testing, order an at-home thyroid test kit to see how your thyroid is performing. 

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