Why Going by TSH Alone Is Inaccurate

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TSH is often regarded as an inaccurate way to measure thyroid function. Why?

TSH (Thyroid Stimulating Hormone) is a pituitary hormone that sends a signal to the thyroid gland. It is produced by the pituitary gland.

It goes like this:

Hypothalamus -(sends signal to)-> Pituitary -(sends signal to)->Thyroid.

With a healthy thyroid, the pituitary gland knocks on the thyroid’s door, signalling it to work and produce so much of certain hormones. It does this by releasing TSH. The thyroid answers the door and does what it’s told by the pituitary by releasing the correct amount of thyroid hormone. Therefore, the pituitary gland isn’t having to knock too much, which equals a low TSH. This is good.

In a person with an underactive thyroid (hypothyroidism), like us, the pituitary gland knocks on the door of the thyroid gland, trying to give orders, but the thyroid ignores it. It doesn’t respond. The pituitary bangs harder and louder and more often on the door, as the thyroid continues to ignore it, and doesn’t produce the hormones it should be. This equals a high TSH. This isn’t good.

Theoretically, if you put the hormones your body is lacking and thyroid is failing to produce, in to your body, the TSH will come down, as the pituitary doesn’t need to knock on the door so much, as it can see that the body is getting the hormones it needs. Doctors see the TSH being low as your body having what it needs. So when you start on thyroid medication and it brings your TSH down, this what makes a doctor so giddy.

Another analogy you could use when your doctor tells you your TSH is fine, but you don’t feel ‘fine’; Would you be happy with a heating engineer telling you your central heating is working fine, just because the thermostat reading is normal, when the radiators are cold and the house is freezing?

Having a ‘fine’ TSH is one thing, however, your body actually performing properly is another. TSH is a pituitary hormone, not a thyroid hormone. It does not tell you your actual thyroid hormone levels, it just gives an inaccurate indication when used alone. You need Free T3 and Free T4 testing to check your actual thyroid hormone levels.

Therefore, you can still feel rubbish with a ‘normal’ TSH because:

  • Your body could be failing to convert the T4 (thyroxine, also known as Levothyroxine and Synthroid in the UK) to T3, which makes you feel rubbish, still. T4 is the storage hormone, T3 is the active hormone, what is actually used.
  • Your Free T3 and T4 levels could be below optimal or at the bottom of the range.
  • Your adrenal glands could be dysfunctioning or you have low iron levels, meaning the T3 isn’t being carried to all your cells, organs and muscles etc. adequately. This can show as a low TSH, but high Free T3 levels on blood results. This is referred to as ‘pooling’ by Stop The Thyroid Madness.

So, the next time your TSH is ‘fine’ and you still feel poop, one of these could well be why! Many thyroid patients find that whilst their TSH is OK, their Free T3 and Free T4, or even Reverse T3 isn’t optimal and so they still feel unwell. Now you know all of this, please don’t stay undiagnosed, under-medicated or be dismissed due to just having TSH tested. Get a copy of your test results and have a look for yourself.

You need to ask for a Full Thyroid Panel blood test to be done for a proper look at how you’re doing, but remember, it’s recommended by many thyroid patients out there to not take your thyroid meds for that day until AFTER the blood has been taken.

Many patients find that while their TSH is OK, their Free T3 and Free T4, or even Reverse T3 isn’t optimal.

Don’t stay undiagnosed, under-medicated or be dismissed due to just having TSH tested.

You can click on the hyperlinks in the above post to learn more and see references to information given.

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Written by Rachel, The Invisible Hypothyroidism

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Rachel Hill, Thyroid Patient Advocate, blogger and author, has Six 2018 WEGO Health Award Nominations. She is a highly ranked writer appearing in the Top Hypothyroidism Websites and Top Thyroid Websites and has worked with The National Academy of Hypothyroidism, The BBC, The Mighty, Yahoo, MSN and ThyroidChange, to name just a few. She is well-recognised as a useful contributor to the thyroid community and also contributed the foreword to Emily Kyle’s The 30-Minute Thyroid Cookbook.

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