The thyroid gland may be small – roughly the size and shape of a butterfly – but its impact on your health is enormous. Located at the front of your neck, just below your Adam's apple, this gland produces hormones that influence virtually every cell, tissue, and organ in your body. From regulating your metabolism and body temperature to affecting your heart rate and mood, the thyroid plays a central role in keeping your body functioning optimally.
When your thyroid isn't working properly, it can cause a wide range of symptoms that are often mistaken for other conditions or simply attributed to stress, ageing, or lifestyle factors. Understanding the signs of thyroid dysfunction can help you recognise when testing might be warranted.
How Your Thyroid Works
Your thyroid produces two main hormones: thyroxine (T4) and triiodothyronine (T3). T4 is the primary hormone produced by the thyroid, but T3 is the more active form. Most T4 is converted to T3 in your tissues.
The production of thyroid hormones is controlled by a feedback loop involving the pituitary gland in your brain and the hypothalamus. When thyroid hormone levels drop, the pituitary releases Thyroid Stimulating Hormone (TSH), which signals the thyroid to produce more hormones. When levels are adequate, TSH production decreases.
This is why TSH is often the first test used to assess thyroid function. High TSH typically indicates an underactive thyroid (the pituitary is working hard to stimulate more hormone production), while low TSH suggests an overactive thyroid.
Hypothyroidism: When Your Thyroid Is Underactive
Hypothyroidism occurs when your thyroid doesn't produce enough hormones to meet your body's needs. This is the most common thyroid disorder, affecting women more frequently than men, and becoming more common with age.
Common causes of hypothyroidism include:
Symptoms of an underactive thyroid may include:
Because hypothyroidism develops gradually, many people don't notice the symptoms at first, or they attribute them to getting older or being busy. The symptoms can also be vague and overlap with many other conditions, which is why testing is so important.
Hyperthyroidism: When Your Thyroid Is Overactive
Hyperthyroidism occurs when your thyroid produces too much hormone, essentially putting your metabolism into overdrive. While less common than hypothyroidism, it can cause significant symptoms and health issues if left untreated.
Common causes of hyperthyroidism include:
Symptoms of an overactive thyroid may include:
Who Should Consider Thyroid Testing?
While anyone can develop a thyroid disorder, certain factors increase your risk:
Understanding Thyroid Function Tests
A thyroid function test typically measures:
TSH (Thyroid Stimulating Hormone) – This is usually the first test performed. It's very sensitive to changes in thyroid function and can detect problems before T4 or T3 levels become abnormal.
Free T4 (Thyroxine) – Measures the unbound, active form of T4 in your blood.
Free T3 (Triiodothyronine) – Measures the active thyroid hormone. Sometimes tested if TSH is abnormal but T4 is normal.
Thyroid antibodies – Tests for TPO antibodies and thyroglobulin antibodies can help diagnose autoimmune thyroid conditions like Hashimoto's or Graves' disease.
What Abnormal Results May Indicate
High TSH with low T4: Primary hypothyroidism – your thyroid isn't producing enough hormones
Low TSH with high T4 and/or T3: Primary hyperthyroidism – your thyroid is producing too much hormone
Low TSH with normal T4/T3: Subclinical hyperthyroidism – may need monitoring
High TSH with normal T4: Subclinical hypothyroidism – may need monitoring or treatment depending on TSH level and symptoms
Preparing for Your Thyroid Test
One advantage of thyroid function tests is that fasting is not required. You can eat and drink normally before your appointment. However, there are a few things to keep in mind:
Getting Tested at Private Blood Tests London
At our South Kensington clinic, we offer comprehensive thyroid function testing. The blood draw takes just a few minutes, performed by our experienced nursing team. We provide the raw test data directly to you.
Learn more about [private blood tests for thyroid problems](/blog/private-blood-tests-for-thyroid-problems-what-you-need-to-know), [can low thyroid cause headaches](/blog/can-low-thyroid-cause-headaches), and explore our [thyroid test services](/thyroid-test).
As a self-referral clinic, you can book thyroid tests directly without a GP referral. We do not provide interpretation of results. We recommend sharing your results with your GP or healthcare provider who can interpret them in the context of your overall health and advise on any treatment or further investigation if needed.
The Importance of Early Detection
Thyroid disorders are very treatable, but left undiagnosed, they can lead to serious health problems. Untreated hypothyroidism can contribute to heart disease, infertility, and in severe cases, a life-threatening condition called myxoedema coma. Untreated hyperthyroidism can cause heart problems, brittle bones, and thyroid storm – a dangerous escalation of symptoms.
If you're experiencing symptoms that could indicate a thyroid problem, or if you have risk factors for thyroid disease, testing can provide valuable information about your health. Many people find peace of mind in knowing their thyroid is functioning normally, while others discover a treatable condition they weren't aware of.
Supporting Your Thyroid Health
While some thyroid conditions require medical treatment, certain lifestyle factors support overall thyroid health:
Remember, if you have a diagnosed thyroid condition, always follow your healthcare provider's advice regarding treatment and monitoring.