The Thyroid: Metabolic Command Centre

Because of this important role, if the thyroid gland isn’t working properly, the consequences can be very wide ranging. The thyroid can become both underactive (when it secretes too little hormone which is known as hypothyroidism) or overactive (when it secretes too much hormone which is known as hyperthyroidism). Either situation can cause you to suffer a long list of different symptoms.

Underactive thyroid

Put simply, if the thyroid is underactive then everything tends to slow down. This leads to people feeling tired all the time, feeling cold all the time, feeling depressed, experiencing dry skin, brittle nails and hair loss. It can also cause heavy or irregular periods. It can even cause slow thoughts and movements. Left untreated, which thankfully is an extremely rare situation these days, it can eventually cause coma and death.

Overactive thyroid

In contrast to hypothyroidism, hyperthyroidism it tends to make everything speed up. An overactive thyroid can make people lose weight, feel hot all the time, feel jittery and anxious, develop a tremor in their hands, and it may cause a racing and irregular heartbeat.

Because a malfunctioning thyroid can cause so many different problems, thyroid function tests are performed by doctors very often.

So why does it go wrong?

The most frequent cause of thyroid problems is autoimmune disease. Autoimmune disease occurs when the immune system mistakenly recognises the body’s own cells as ‘foreign’ and so attacks those cells in the same way as it attacks infectious organisms. There are numerous different autoimmune diseases, each causing symptoms that depend on the cells that are getting attacked, but thyroid diseases are amongst the commonest.

Genetic autoimmune diseases

What triggers these diseases remains a mystery, but genetics certainly play a part. We see autoimmune diseases running in families, and unfortunately some people suffer a number of different autoimmune diseases together. Women are generally more susceptible to autoimmune diseases, and this is certainly true of thyroid disease.

Hashimoto Thyroditis

The commonest cause of an underactive thyroid is known as ‘Hashimoto’s Thyroiditis’ (thyroiditis just means inflammation of the thyroid). The commonest cause of an overactive thyroid is ‘Grave’s disease’. Both are named after the doctors who first described them.

In hyperthyroidism the reverse is true. Because levels of T3 and T4 are already too high, the brain stops producing TSH so TSH levels fall and may become virtually undetectable.

How do you test thyroid function?

A variety of things are tested to assess the thyroid. Firstly, we can test the levels of hormones secreted by the thyroid. These are known as triiodothyronine and thyroxine or, more conveniently, as T3 and T4. These are the hormones that circulate in the bloodstream and tell cells all around the body how they should be behaving. Low levels of these hormones indicate hypothyroidism, and high levels suggest hyperthyroidism.

We also usually test for a hormone that is secreted by the pituitary gland in the brain called ‘Thyroid Stimulating Hormone’ or TSH. As you might expect, the brain is in overall control, and it uses TSH to tell the thyroid what to do. If the thyroid is underactive, then the brain produces more and more TSH in an effort to make the thyroid do its job. So, in hypothyroidism we usually see low T3 and T4 and high TSH.

Sometimes levels of T3 and T4 are normal but the TSH is high. This means the thyroid is still producing enough hormone, but the brain is having to work very hard to make it do so. This is known as ‘subclinical hypothyroidism’ because at this stage you will probably not be experiencing any symptoms, but the thyroid is not working at 100%. If your blood tests show subclinical hypothyroidism, then it is usually a good idea to monitor your thyroid function regularly because you may develop full blown hypothyroidism at some point.

The last common test that we do is an antibody test against an enzyme called Thyroid Peroxidase (TPO). TPO is an enzyme produced in the thyroid that is involved in the production of thyroid hormones. The presence of TPO antibodies confirms an autoimmune cause of thyroid disease. It is also possible to have a healthy thyroid but still have TPO antibodies. This doesn’t necessarily mean that you will go on to develop thyroid disease, but the risk of doing so is higher so it is usually wise to have your thyroid function checked each year if this is the case.

There are a number of other thyroid antibodies that can be tested, and these are usually checked depending on specific circumstances.

What if the results are abnormal?

Thyroid diseases are fairly common and, fortunately, they can be treated, so abnormal tests need not be a cause for panic. In the first instance, it is usually sensible to repeat the tests. Abnormal tests that return to normal are not that uncommon. For example, sometimes thyroid function is disturbed due to an acute illness so we usually recommended testing it after any symptoms of a short term illness are over.

If the repeat tests confirm a problem, or the first test is abnormal and you have obvious thyroid symptoms, then you should speak to your doctor. It should be possible to get you feeling better quite quickly.

How often should thyroid function be tested?

The frequency of thyroid function testing depends on several factors, including the person's age, medical history, and current thyroid status. In general, thyroid function should be tested:

1. If a person is experiencing symptoms of thyroid dysfunction, such as weight changes, fatigue, hair loss, or mood changes.

2. If a person has a family history of thyroid disease or has had previous thyroid problems.

3. If a female is pregnant or planning to become pregnant, as thyroid function can impact fetal development.

4. If a person is taking medication that can affect thyroid function, such as lithium or amiodarone.

5. If a person has undergone thyroid surgery or radiation therapy.

The British Thyroid Foundation recommends that thyroid function is tested regularly, generally yearly. However, the frequency of testing may be higher for those with an increased risk of thyroid disease or who are experiencing symptoms of thyroid dysfunction. It is always best to consult with your GP to determine the appropriate testing frequency based on individual circumstances.

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