What Does Borderline/Subclinical Hypothyroid Mean?

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Originally published on 9th July 2016
Last updated on 28th October 2018

I hate the term ‘borderline hypothyroid’ or ‘subclinical hypothyroidism’. It leaves many people undiagnosed and ill. Many just get worse and worse with time. 

A someone who was diagnosed with a ‘borderline underactive thyroid’, I always wince at the phrase. Although my TSH test may have been borderline, my symptoms certainly were not. In fact, I was told, when at a point of barely functioning anymore, to come back in a few months time for a repeat thyroid test to be reviewed again. Because I wasn’t yet ‘bad enough’ to receive treatment.

To no surprise, when I returned a few months later, I was feeling absolutely dreadful. And I looked absolutely dreadful! By the time of the repeat test, my results were only slightly worse and still ‘mildly’ hypothyroid, but I was started on Levothyroxine to see if it helped because I complained about my symptoms enough. By which time, the Levothyroxine didn’t help me anyway. 

In my opinion, I feel that the term ‘borderline hypothyroid’ or ‘subclinical hypothyroidism’ used when a doctor refuses treatment, is them acknowledging your thyroid isn’t performing great, but not yet bad enough to receive medication. It’s like a limbo stage and it is disgusting to leave people there, without any further support or guidance on their health. Some stay in this limbo for years, going back to the doctor numerous times only to be told they’re still ‘borderline’ and refused any further help.

The problem is that many doctors just go by TSH when testing thyroid function, which isn’t accurate on its own, and while this can only be ‘mildly’ bad, Free T3 and Free T4 levels can be much lower and these are the actual thyroid hormone levels, with TSH being a pituitary hormone. TSH stands for ‘Thyroid Stimulating Hormone’ and is a hormone secreted by the pituitary gland. It serves as an average read out over the previous four to six weeks of your thyroid levels but doesn’t give the most accurate view of things when used alone.

Being optimal in thyroid hormone levels can make all the difference for a lot of people, but subclinical or borderline hypothyroidism leaves many people with low levels in Free T3 and Free T4, causing ongoing symptoms, because they are actually hypothyroid. And it’s important to keep in mind that lab ranges differ from lab to lab and country to country. The inconsistency on what constitutes for ‘borderline’ hypothyroidism is shocking.

Not only is going by TSH alone inaccurate in diagnosing and treating hypothyroidism, but subjecting everyone to outdated ranges is problematic since may of us see the effects of a high TSH differently. For example, the range my doctor used was 0.5-5, and I felt very very ill at 6, which is just above range; borderline. I’ve heard some people get to a TSH of 4, 50 or even 100 before feeling unwell, therefore, we should be treated individually. Ranges also differ from lab to lab.

A TSH of 2 or below to reduce symptoms is recommend by many these days, so even if you’re classed as borderline with a TSH reading of 6 on a 0.5-5 range, then this can be causing you a lot of symptoms. The same goes for a Free T4 of 11 when the range is 10-20, for example. These ranges do not take in to account where each individual feels best and doctors should be working to find this sweet spot for each patient, when they show classic hypothyroid symptoms. We’re individuals and deserve to be treated as such.

Since we didn’t have our TSH, Free T3 and Free T4 levels tested when our thyroid function was good, we don’t know our individual optimal levels, so we must work to find these.

If your doctor has said you’re borderline or subclinically hypothyroid, then I strongly suggest you get another doctors opinion, and possibly another, until you’re happy. You should also have a retest of any borderline/subclinical TSH, Free T3 or Free T4 readings to see if they have gotten better or worse. They can occasionally get better, but for many, they get progressively worse.

It is also worth noting that Hashimoto’s, an autoimmune disease that causes about 90% of all hypothyroid cases, can cause TSH levels to swing, so if you still feel unwell and have blood test results that seem to get better and worse again, it’s likely you have Hashimoto’s, which definitely needs addressing. I therefore support everyone who has or thinks they have thyroid issues, to also test TGAB and TPOAB.

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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2 thoughts on “What Does Borderline/Subclinical Hypothyroid Mean?

  1. Great article. What about when TSH is super low but FT3 and FT4 are optimal? My GP wants to keep reducing my meds as he thinks I’m hyper due to the TSH, however I know I’m not hyper.

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