Thyroid Test

Thyroxine (T4) is a hormone made by the thyroid gland. We measure levels of Free T4, which is a key marker for thyroid function.

We also measure Thyroid-stimulating hormone (TSH) which is the pituitary (brain) hormone that controls the thyroid gland.

The thyroid gland is a butterfly shaped endocrine gland that’s located in the front part of the neck just below the Adam’s apple. The thyroid gland plays a vital role in the metabolism, development, and regulation of the human body. It uses iodine from the food we eat (an element that the body can’t make on its own) to produce the key thyroid hormones, triiodothyronine (also known as T3) and tetraiodothyronine (also called thyroxine or T4). The thyroid gland also makes the peptide hormone calcitonin. The former two are what are referred to as “thyroid hormones” made by this gland and they play a crucial role influencing aspects such as the body’s weight, internal temperature, energy levels, skin, hair and nail growth among others¹.

Depending on the state in which the body is in, the requirement for more or less of the thyroid hormones is finely balanced. To ensure the right amount of hormonal balance, the thyroid gland relies on the pituitary gland to signal whether to release more or fewer hormones into the bloodstream. For instance, increased production of T3 and T4 may be needed to boost the body’s metabolic rate if it slows.

Every cell in our bodies relies on thyroid hormones to regulate its metabolism. The thyroid gland produces about 80% tetraiodothyronine (thyroxine or T4) and 20% triiodothyronine (T3). Thyroxine (T4) is the primary thyroid hormone that’s responsible for metabolism, mood, energy levels, and body temperature, among other things. Triiodothyronine (T3) is the hormone that influences digestion, metabolic function, and bone, nail, and hair health.

Both T3 and T4 circulate in the blood stream bound to proteins such as albumin and thyroxine-binding globulin (TBG). When these hormones are bound to proteins they are inactive. It is only the free unbound T3 and T4 that are active and can be effective. These are called Free T3 (FT3) and Free T4 (FT4) respectively. The FT3 and FT4 represent only a very small percentage of the total thyroid hormones and measurement of these free hormones is very specialist but very important.

As mentioned above, the thyroid gland is influenced by the pituitary gland, a small peanut-sized gland located at the base of the brain. When thyroid hormone levels drop too low, the pituitary gland will produce more of what is called Thyroid Stimulating Hormone (TSH) which is responsible for stimulating the thyroid gland into manufacturing more T3 and T4.

Sometimes the body needs more or less of the thyroid hormones which can be compared to a “heat source”. The thyroid gland itself acts like a furnace while the pituitary gland serves as the thermostat control. When more hormones are needed, the pituitary gland signals to the thyroid gland via TSH to produce and secrete T3 and T4 into the bloodstream. The pituitary gland is regulated by the hypothalamus, which is also found in the brain and is the primary dictator of both the pituitary gland and the thyroid gland’s activity. The hypothalamus produces TSH Releasing Hormone (TRH) which communicates to the pituitary gland to release TSH and stimulate the thyroid gland into generating more T3 and T4.

In the cohesive, hormone-regulating system that involves the hypothalamus, pituitary gland, and thyroid gland, thyroid-stimulating hormone (TSH) plays an important role that can affect everything from your appetite and digestion to your fertility and mood. Also known as thyrotropin, thyroid-stimulating hormone controls the way other hormones function. As the name implies, this hormone stimulates the production of two primary thyroid hormones, T3 and T4.

The process starts from the hypothalamus, which produces thyrotropin-releasing hormone (TRH), thereby controlling the pituitary gland and the production of thyroid-stimulating hormone (TSH) itself. When the pituitary gland is triggered to make TSH, it’s then released into the bloodstream and eventually binds to the cells of the thyroid gland. After TSH binds to the cells, the thyroid gland is signaled to manufacture appropriate amounts of T3 and T4. Simultaneously, T3 and T4 have the ability to send a negative feedback loop to the pituitary gland to stop TSH production and maintain balanced hormones levels.

What is a Normal TSH Level?

With any thyroid-related blood test, TSH levels are often the first thing to be measured. If TSH levels are normal, then in most cases an individual has a properly-functioning thyroid.

For both men and women, the normal range of TSH level typically falls between 0.27 – 4.2 mU/L. Keep in mind, age and pregnancy are two common variables that can influence the normal range of TSH levels. Young children, especially babies, will often as normal have a much higher TSH normal range. Pregnant women will experience different levels of TSH depending on the trimester; this is mainly due to the fact that they have higher levels of circulating proteins.

What Does High TSH Mean?

If your TSH levels are measured high after a blood test, this usually indicates that your thyroid is underactive, or is not producing enough thyroid hormones. If TSH levels are higher than normal then it’s common that a blood test for free thyroxine (FT4) will also be measured. High TSH levels along with low FT4 will suggest an underactive thyroid, a condition referred to as hypothyroidism.

In many cases, an individual’s TSH level may be slightly high but the FT4 level falls within the normal range. This is called subclinical hypothyroidism which is a mild form of thyroid failure. Because even subclinical hypothyroidism can gradually worsen to becoming clinical hypothyroidism over time, it’s best to take prompt action and seek further testing and follow up. Only a TSH and FT4 test can find this out.

What Does Low TSH Mean?

When a blood test indicates that TSH levels are low an individual may have an overactive thyroid that’s producing too many thyroid hormones. This is called hyperthyroidism and is confirmed by also testing FT4 level. Low TSH and high FT4 levels suggest an overactive thyroid. Low TSH can also indicate the potential failure of the pituitary gland, which is responsible for TSH release and balancing the production of thyroid hormones. This pituitary failure will result in a low FT4 level.

In some cases, doctors may also choose to test free triiodothyronine (FT3) levels along with FT4. This is sometimes done as a next step when testing for hyperthyroidism; for example to look for T3 toxicosis when sometimes the FT4 is normal but the FT3 level is high.

What is a TSH Blood Test?

A thyroid-stimulating hormone (TSH) blood test is the key way of accurately measuring your thyroid hormone status and effectively pinpointing whether there’s a problem. It also provides and easy testing method, as at-home TSH blood test kits make it convenient to measure TSH with a simple finger prick method.

In simple terms, a TSH blood test is used to evaluate how well the thyroid gland is working in relation to the pituitary gland. Not only will a thyroid blood test measure a TSH level (which helps assess a healthy functioning pituitary gland) but in most cases, thyroid blood tests will also measure free thyroxine (FT4) to assess how well the pituitary gland and thyroid gland are working together. These metrics combined (TSH and FT4) tell a full story behind an individual’s thyroid health and what action, if any, is needed to balance for example a low TSH and high FT4, or high TSH and low FT4.

Both hypothyroidism and hyperthyroidism are prevalent forms of thyroid disease that impact millions of individuals throughout the world. In fact, the prevalence of hypothyroidism alone in the UK is about 2% of the population. Even more stark is that hypothyroidism is 5-². While hypothyroidism is more common than hyperthyroidism, both are common thyroid problems worth discussing.

The fundamental difference between hypothyroidism vs hyperthyroidism is simple. Hypothyroidism refers to an underactive thyroid gland (that does not produce enough thyroid hormone) and hyperthyroidism refers to an overactive thyroid gland (that produces too much thyroid hormone). The root word “hyper” defines a condition that involves an excess or too much of something, in this case a thyroid hormone excess. Conversely, the “hypo” in hypothyroidism refers to a thyroid hormone deficiency.

Hyperthyroidism is a term used to describe any condition of the thyroid in which too much hormone is being produced. In simple terms, hyperthyroidism or high thyroid levels means having an overactive thyroid gland. Similarly, the term thyrotoxicosis has a related meaning referring to high thyroid hormone levels present in the body, regardless of the source. Hyperthyroidism, however, specifically delineates the thyroid gland as being overactive and thereby the source of excessive thyroid hormone levels.

What Causes Hyperthyroidism?

The most common cause of hyperthyroidism across a majority of individuals is overproduction of thyroid hormone (triiodothyronine and thyroxine) by the thyroid gland, a condition most commonly known as Graves’ disease. Graves’ disease, which makes up of all hyperthyroid cases, is an autoimmune disorder caused by antibodies in the blood that stimulate the thyroid gland, causing it to grow in size (sometimes forming what’s called a goitre) and secrete an excess of thyroid hormone in the bloodstream.

Another form of hyperthyroidism occurs when one or more nodules of the thyroid gland gradually grow both in size and activity, resulting in an abnormally high output of thyroid hormone production into the bloodstream. This condition, which is less common, can be known as multinodular goitre or toxic nodular goitre. Some individuals may experience hyperthyroidism symptoms through a condition called thyroiditis. This is also an autoimmune problem involving the immune system.

What are the Symptoms of an Overactive Thyroid?

Because thyroid hormone has a whole-body influence over many metabolic processes, the symptoms of hyperthyroidism can manifest in many different ways. The onset of hyperthyroidism generally begins slowly but can evolve abruptly. The symptoms may be mistaken for anxiety or nervousness due to stress but can grow in severity. Some of the most common hyperthyroid symptoms include:

– feeling nervous, anxious, moody, or irritable

– fluctuating energy levels, often severe fatigue and tiredness

– difficulty sleeping

– thinning hair and skin

– muscle weakness

– more frequent urination and bowel movements

– increased perspiration

– heart racing and hand tremors

– lightened menstural flow

With Graves’ Disease, the most common form of hyperthyroidism, the upper eyelids may appear enlarged and elevated, and one or both eyes may bulge. Additionally, some severe cases of an overactive thyroid will cause a goitre or significant swelling of the front or side of the neck from an enlarged thyroid gland.

How to Test for Hyperthyroidism?

The most accurate and efficient way to test for hyperthyroidism is a standard blood test that measures free thyroxine (FT4) and thyroid-stimulating hormone (TSH). These metrics alone can generally confirm a diagnosis of hyperthyroidism. Low or nonexistent amounts of TSH and high levels of FT4 point to an overactive thyroid gland. The amount of TSH is an important measurement in a thyroid test because it’s the key hormone that signals your thyroid gland to produce more T4.

If a blood test confirms hyperthyroidism, your GP may recommend follow-up testing to help pinpoint why the thyroid gland is overactive. These additional tests may include a radioiodine uptake test (which measures how much iodine the thyroid absorbs over a period of time) or a thyroid ultrasound (produces images to show up thyroid nodules).

How to Treat Hyperthyroidism?

There are several different hyperthyroidism treatments. The best course of treatment will depend on the underlying cause and severity of the hyperthyroidism as well as the individual’s age, physical condition, and personal preferences. The most common treatments for hyperthyroidism include:

• Radioactive iodine. A procedure where the radioactive iodine is given orally and is absorbed by the thyroid gland, causing the gland to decrease in size. The symptoms generally subside within several months.

 

• Anti-thyroid medications. Medications are intended to prevent the thyroid gland from producing excess amounts of hormones and relieve hyperthyroidism symptoms. Methimazole (Tapazole) and propylthiouracil are some anti-thyroid medications.

 

• Thyroidectomy surgery. While often a last resort (e.g. for individuals who can’t tolerate radioactive iodine, such as pregnant women) a thyroidectomy involves the removal of part of the thyroid gland. This surgery comes with some risk and potential lifelong medication to normalize thyroid hormone levels, depending on the extent.

Unlike hyperthyroidism where the thyroid gland is overactive, hypothyroidism is characterized by having lower than normal thyroid hormones in the bloodstream due to an underactive thyroid gland. Because the primary thyroid hormones (TSH, T4, and T3) are vital for many metabolic processes, hypothyroidism can affect the body in a number of ways, ranging from energy levels, temperature regulation, or specific organ functions. While hypothyroid symptoms may be more subtle and difficult to detect, some individuals with an underactive thyroid may feel more easily tired, depressed, forgetful, cold, or experience irregular bowel movements.

What Causes Hypothyroidism?

An underactive thyroid gland resulting in hypothyroidism can be caused by many possible contributors, including:

• Autoimmune disease: gradually or suddenly, the immune system can attack and damage the thyroid gland. Hashimoto’s thyroiditis and atrophic thyroiditis are common autoimmune diseases that can cause hypothyroidism.

 

• Thyroid inflammation: referred to as “thyroiditis,” this inflammation of the thyroid gland, which inhibits the thyroid from functioning properly, is often the result of a viral infection or autoimmune attack.

 

• Surgery: removal of part or all of the thyroid gland, typically as a result of Graves’ disease or thyroid cancer, can contribute to hypothyroidism.

 

• Pituitary gland damage or disease: As the source of TSH, which tells the thyroid gland to produce more T3 and T4 hormones, any disruption to the pituitary gland can result in an underactive thyroid gland.

 

• Radiation treatment: When used to treat cancers of the head and neck, radiation treatment can disrupt normal functioning of the thyroid gland, thereby resulting in hypothyroid symptoms.

 

Other causes of an underactive thyroid gland can be medication-related (e.g. amiodarone and lithium which can disrupt the thyroid from working normally),

What are the Symptoms of an Underactive Thyroid?

Symptoms of hypothyroidism can be subtle and difficult to detect. Some individuals may have no symptoms at all, while others can experience moderate to severe symptoms. Among the most commonly reported symptoms of an underactive thyroid include:

– fatigue and fluctuating energy

– weight gain

– feeling unusually cold

– dry skin, brittle nails and hair loss

– poor cognition or memory

– depression and mood fluctuation

– muscle aches and joint pain

– constipation

– irregular periods

– enlarged thyroid gland (goitre)

It’s worth noting that these hypothyroid symptoms can be ambiguous in attributing specifically to an underactive thyroid gland. A proper blood test measuring TSH and free thyroxine (FT4) levels can diffuse any confusion by validating a case of hypothyroidism.

How to Test for Hypothyroidism?

Like hyperthyroidism, the best way to test for hypothyroidism is a blood test measuring both thyroid-stimulating hormone (TSH) and free thyroxine (FT4). Having abnormally high levels of TSH and low levels of FT4 is an indication of primary hypothyroidism. Slightly elevated TSH with normal FT4 is known as borderline or subclinical hypothyroidism.

Cases in which a thyroid test shows low TSH and low FT4 often indicate secondary or central hypothyroidism. This means that your pituitary gland and thyroid gland are both having problems producing normal hormone levels.

How to Treat Hypothyroidism?

Hypothyroidism is generally treated by replacing the amount of hormone that the thyroid gland can no longer make, thereby elevating thyroxine and TSH levels back to normal. T4 replacement can help restore the body’s thyroid hormone levels and overall function. This form of hypothyroidism treatment is the most common and is effective for most patients with an underactive thyroid gland.

What Foods Are Good for Hypothyroidism?

While no specific foods or dietary supplements have been reported to effectively help hypothyroidism, it’s generally recommended to consume a healthy diet that’s rich in fruits, vegetables, and quality sources of fat and protein.

Thyroid blood tests are an easy and effective way to measure the amount of thyroid hormones in your blood, which can help determine whether your thyroid gland is functioning properly. Thyroid blood tests are often conducted in a clinical setting, such as by giving a blood sample at your doctor’s or at hospital. They’re also made available through at-home thyroid test kits. In the case of the latter, it’s important the test kit provider handles and tests the blood samples in a suitably certified laboratory   to ensure quality control.

How Much Does a Thyroid Test Cost?

The cost of a thyroid test will depend on what the panel includes and where the testing is conducted. Thyroid tests are available on the NHS but sometimes thyroid levels aren’t always checked as standard. At-home thyroid test kits provide a much more convenient option.

How Long Does it Take to Get Blood Test Results for Thyroid?

The turnaround time to get your blood test results varies based on the provider but generally takes between one and two weeks. With an at-home Thyroid Test from YorkTest, you will receive your blood test results indicating thyroid hormone levels within 7 days.

Do You Have to Fast for a Thyroid Test?

No, fasting is not recommended for a thyroid test.

What size of blood sample is needed for a Thyroid Test?

Most laboratories require a full blood draw from your arm for a thyroid test. For the YorkTest thyroid test only a few drops of blood are required from a finger-prick. A full set of instructions for the thyroid test are included with the blood collection kit and the sample collection is straightforward. The sample is put in the post to the accredited laboratory.

 

References

¹ British Thyroid Foundation https://www.btf-thyroid.org/

² NICE Guidelines: Thyroid disease: assessment and management https://www.nice.org.uk/ November 2019