Thyroid Hormone Testing - An Overview of The Pitfalls and why 'normal' might not be 'normal'

The following is a brief overview of some of the issues with thyroid testing in the UK, relating specifically to people with an under-active thyroid.

Thyroid hormone testing is a thorny subject and sometimes a tricky one to discuss in clinic.  I often see clients who have already been tested by their GP, and are told that their thyroid results are 'normal'. I usually inwardly cringe at this point, and then ask 'What were your levels, and what was measured?' whilst already knowing the reply. The answer is usually 'I don't know, but I've been told I'm fine'  However, the client doesn't feel fine, and often has all the symptoms of sub-optimal thyroid. What we really need to know is their actual results, and quite often, we need to do more in depth testing to gain a deeper understand of what might be going on.

What usually happens when you have your thyroid checked is that TSH (Thyroid Stimulating Hormone), and possibly fT4 (free T4) are tested.

TSH is produced by the pituitary gland in the brain, and directs the thyroid gland to produce thyroid hormones, of which T3 and T4 are biologically active. T4 is the most abundant, but not the most biologically active thyroid hormone. Total T4 is also sometimes measured, but 'free' T4 represents the amount of the total hormone available to the body. Same with T3, free T3 is the amount available to the body and therefore this is what's measured.

If TSH is too high, you may be told you have an under-active thyroid, or that you are hypothyroid, and that you may need to take thyroxine, especially if paired with low fT4. If TSH is within the reference range and fT4 is also within range, it is likely you will be told you're normal, unless you have a good GP who will do more in-depth testing. You may be told you are 'borderline' and that re-testing further down the line may be appropriate.

However, there are a couple of issue with this.

Firstly, the reference ranges are wide, and vary by lab.

TSH = 0.4 - 5 miU/L. However, functionally optimum, is considered to be less than 2.0 from a functional medicine perspective
fT4 = 9 - 25 pmol/L. So what happens if you were at 22, but you're now at 10?

Secondly, these markers alone don't give a full picture. fT3 is the most biologically active thyroid hormone. Our thyroid gland produces around 20% of fT3, but the rest is converted from fT4 into fT3. This happens predominantly in the liver and kidneys by deiodinase enzymes. These enzymes require selenium and zinc, amongst other nutrients to function.

Therefore, if you are low in selenium and zinc etc, you may not be able to produce sufficient fT3 even if you have sufficient fT4. So you can see why just measuring fT4 doesn't give the full picture. There are also other factors which can hamper the conversion of fT4 into fT3 including stress and either too much or too little of the hormone cortisol. Hormone replacement therapy (HRT) can also affect thyroid conversion.

In addition, in times of high stress, trauma, illness etc, our body can cleverly try to slow us down by producing something called rT3 or Reverse T3. This blocks our receptors for fT3, so that it can't be used. This is not something tested in the NHS as routine.

A further consideration is that the majority (arguably around 80%) of clients with hypothyroidism are actually suffering with an autoimmune condition called Hashimoto's, where the immune system attacks our own thyroid gland.  If you are fortunate, your GP will measure anti-thyroid peroxidase antibodies (anti-TPO), and anti-thyroglobulin antibodies (anti-TG) at the outset and give you this diagnosis. I have personally found my GP will do this on request. However, this often won't be measured, as the only available treatment on the NHS for hypothyroidism is synthetic thyroid hormone, usually thyroxine, so unless you have high TSH or low fT4, there is no treatment, so no reason to test antibodies, which means you could be suffering with an autoimmune condition that is giving you symptoms, but you have not been diagnosed. (This is the worst case scenario, some practices are more thorough!)

This is where a functional medicine approach can help.

Firstly, there are private tests available that will measure the above markers i.e. TSH, Free T4, Free T3, Reverse T3, and anti-thyroid antibodies. Although no tests are perfect, and whilst we may be producing thyroid hormones, we don't yet have  a perfect to test to assess whether our cells are using them effectively.

Secondly, we work to  identify the root cause or causes of the autoimmune condition, or underactive thyroid.  Where Hashimoto's is identified, we would consider the reasons WHY the immune system has started to over-react, and started to attack the thyroid. This could be due to genetics, underlying unidentified infections (viral, parasites, bacterial, fungal), high toxic metal burden, stress, trauma, food intolerances and sensitivities, or quite often, a combination of these.

This is different for each client. We then work with our clients to put a plan in place that seeks to address the underlying imbalances, removing the contributory factors where possible and helping the client reach optimum health.

If you'd like further help or would like to know more about how I work, then please get in touch for a free 15-minute assessment call on 07909 732017 or email alexis@alexispriornutrition.com