The thyroid is an often overlooked but surprisingly important gland located at the base of the neck. Glands produce biological substances which have an effect on other parts of the body.
There are two types of gland: endocrine and exocrine. The latter produce substances that are secreted through a duct onto the surface of the body: for example, sweat. Endocrine glands, meanwhile, produce substances which circulate through the bloodstream.
The thyroid produces three hormones – chemical messengers – and two of these play very important roles in the healthy functioning of our bodies. Triiodothyronine and thyroxine play a role in multiple functions central to life. For example:
- Our body’s response to chemical neurotransmitters: these send signals from one nerve to the next
- The functioning of muscles
- Metabolism – the fundamental chemical processes within our cells that sustain life and generate heat
- The growth of nerve cells and bone
Our bodies make triiodothyronine and thyroxine from the element iodine but the two hormones contain differing levels of this mineral. Thyroxine is often referred to as T4 because it contains four atoms in its structure. This is the ‘default’ thyroid hormone – about 95% of the thyroid hormones in circulation within the average person at any one time will be thyroxine.
Triiodothyronine is a variation of thyroxine with one fewer iodine atom – hence the shorthand name T3. When more is required, the body can generate T3 from T4.
What is a thyroid test?
Thyroid tests are conducted in order to assess whether a person’s thyroid is working correctly. Blood samples taken from the patient are assessed by clinical diagnostic equipment in order to establish the levels of thyroid and other hormones in circulation, and draw conclusions about the current health of their thyroid gland.
Why is it important to have your thyroid tested?
Like any other organ, the thyroid doesn’t always work perfectly, especially as people grow older.
An underactive thyroid, or hypothyroidism, is very common in older people: around one in 20 people develop this condition. Hypothyroidism means the thyroid is not producing quite enough T4 or T3 for optimal health.
People with this condition often report random aches and pains, excessive tiredness, constipation, susceptibility to the cold and even depression.
By contrast, an overactive thyroid is called ‘hyperthyroidism’. Typical symptoms include feeling disproportionately warm, tremors and a racing heartbeat.
Long term, both hypo- and hyperthyroidism damage health and wellbeing. Women are at a particularly high risk of thyroid problems in later life.
It’s worth noting that other factors can influence thyroid hormone levels: for example, hepatitis, steroids, contraceptive pills and pregnancy.
Less frequently seen is Hashimoto’s thyroiditis. This is an autoimmune disorder: i.e. an illness in which the immune system releases antibodies to attack parts of its own body: in this case, the thyroid gland. As we have seen, the thyroid is essential to health so this is a potentially serious disorder requiring medical intervention.
You may also see Hashimoto’s thyroiditis referred to as autoimmune thyroid disease or autoimmune thyroiditis.
Some people experience thyroid nodules. These swellings are usually harmless but can sometimes interfere with breathing or become cancerous.
Eating plenty of iodine is a good way to maximise the chances of your thyroid staying healthy. Foods rich in iodine include:
- Fish – e.g. cod and tuna
- Other seafood – for example shrimp
What tests are there and how do you know which one to choose?
Thyroid testing procedures vary from country to country, but the most frequently conducted are:
T3 and T4 testing
These are straightforward checks for the levels of T3 and T4 in a submitted blood sample. This is done in order to assess whether or not their thyroid is producing a healthy level of these hormones.
FT3 and FT4 testing
Some thyroid tests focus on so-called ‘free triiodothyronine’ and ‘free thyroxine’ – more commonly known as FT3 and FT4. This is the form of these hormones that freely circulates through the bloodstream and which is accessible to organs in different parts of the body. The remaining quantity of thyroid hormone is bound to carrier proteins that help transport them through the body.
TSH level testing
TSH stands for thyroid stimulating hormone and if you’re looking for a deep analysis of TSH tests then follow the link. This is produced by a separate endocrine gland – the pituitary, located in the lower part of the brain. The name is self-explanatory: TSH is produced to stimulate the thyroid into producing its own hormones: T3 and T4, as well as a third one called calcitonin which aids in the digestion of minerals.
TSH levels rise and fall in response to changing levels of the thyroid hormones. Therefore, for example, a high level of TSH may indicate an underactive thyroid.
Doctors typically prescribe TSH and T4 testing for suspected thyroid problems. If abnormal levels are detected, T3 tests may also be conducted.
There is no precise answer to exactly what constitutes a healthy thyroid hormone level. This varies by individual and circumstance, but as a general rule doctors will be looking for T4 levels of 0.9 to 2.3 nanograms per deciliter (ng/dL) and T3 levels of 100 to 200 ng/dL.
TSH levels are more normally measured in milli-international units per litre (mIU/L). If yours are between 0.4 and 4.0 mIU/L, they will be considered normal.
Testing your thyroid at home
You should certainly consult your doctor if your symptoms are significant or seem to be getting worse. In most cases they will refer you on for testing.
But otherwise, there’s no real need to wait. Modern technology means it’s now possible to test your thyroid hormone levels at home. A testing kit like the full thyroid function test from Health Hub is straightforward and painless. Send in your blood sample and receive your results in a matter of days.
Prescription treatments are available for both hypothyroidism and hyperthyroidism. People with the former are normally prescribed hormone supplements to boost blood levels of T4 and T3.
Meanwhile, hyperthyroidism is generally treated with drugs that slow down thyroid hormone production. Surgery is sometimes conducted for more severe cases.