Understanding TSH Testing: A Crucial Tool for Thyroid Health

Thyroid-stimulating hormone testing, or TSH testing, is a cornerstone in the diagnosis and management of thyroid disorders. This is a simple blood test that provides valuable insights into the function of the thyroid gland. It can detect if you suffer from an overactive thyroid (hyperthyroidism) or an underactive thyroid (hypothyroidism). This test can also detect other types of thyroid disorders before you start showing symptoms.

What does my thyroid gland do?

The thyroid is a small gland in your neck that is part of your endocrine system (a complex network of glands and hormones (chemical messengers) that controls how your body functions). Your thyroid manages a wide range of functions, from your growth and development to your moods. It also manages your metabolism, meaning it manages how quickly your body turns food into energy for your cells. To do that, it relies on thyroid-stimulating hormones.

What is TSH?

Thyroid-stimulating hormones (TSH) are produced by the pituitary gland located at the base of your brain. TSH stimulates the thyroid gland to produce other hormones like thyroxine (T4) and triiodothyronine (T3) that help to regulate your body's metabolism. 

The pituitary gland acts as a sensor, adjusting TSH levels based on the amount of thyroid hormones (T3 and T4) in the bloodstream. If a normal pituitary gland detects high levels of thyroid hormones present in your blood, it signals to itself to produce less TSH, thereby modulating the amount of thyroid hormones present in your bloodstream. 

What do my thyroid hormones control?

Thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), play a crucial role in regulating various bodily functions:

1) Metabolism

Thyroid hormones directly influence the rate at which your cells convert nutrients into energy. They increase the basal metabolic rate, determining how many calories your body burns at rest. When thyroid levels are high (hyperthyroidism), you may experience unexplained weight loss despite increased appetite. When levels are low (hypothyroidism), your metabolism slows, potentially leading to weight gain even with reduced food intake.

2) Cardiovascular function

Thyroid hormones can affect both the force and speed of each heartbeat. They also relax the smooth muscle in blood vessel walls, affecting peripheral resistance. With higher thyroid levels, your heart rate increases, potentially causing palpitations or tachycardia. Lower levels can result in a slower heart rate (bradycardia) and higher blood pressure due to stiffer arteries.

3) Body temperature

Thyroid hormones stimulate heat production (thermogenesis) by accelerating cellular metabolism. They increase oxygen consumption and energy expenditure in virtually all tissues, generating heat as a byproduct. This explains why people with hypothyroidism often feel cold, while those with hyperthyroidism may feel excessively warm and have difficulty tolerating heat.

4) Energy levels

Thyroid hormones enhance mitochondrial function, improving the efficiency of energy production. This explains why fatigue and lethargy are hallmark symptoms of hypothyroidism.

5) Growth and development

During pregnancy, maternal thyroid hormones cross the placenta in the first trimester, directing crucial early brain development before the foetal thyroid becomes functional. In childhood, these hormones regulate bone growth, brain maturation, and organ development. Severe thyroid deficiency in infants can lead to cretinism, characterised by stunted physical and mental development.

6) Reproductive health

Thyroid hormones interact with reproductive hormones, affecting fertility in both men and women. In women, they influence ovulation, menstrual regularity, and the production of sex hormone-binding globulin. Thyroid dysfunction is associated with menstrual irregularities, reduced fertility, and complications during pregnancy such as miscarriage or preterm birth.

Learn more about the thyroid’s role in fertility here.

What factors affect my TSH levels?

Several factors can affect your TSH levels:

• Age

  • TSH levels tend to increase in people over 80 years old.

• Pregnancy

  • TSH levels often dip slightly during the first trimester of pregnancy and then start to rise. In general, the normal ranges for TSH levels during different trimesters are as follows:

• Medications and supplements 

  • Many drugs, over-the-counter supplements, and multivitamins can influence TSH levels.

• Lifestyle factors

  • Smoking generally leads to a decrease in TSH levels.

  • Body Mass Index (BMI), Positively correlated with TSH levels.

  • Diet, Iodine intake, particularly excess iodine, can increase TSH levels.

• Thyroid disorders or other health conditions and illnesses

  • Conditions like Hashimoto's disease, Graves' disease, and thyroiditis can significantly impact TSH levels.

• Genetic factors

  • Up to 65% of interindividual variations in TSH levels can be attributed to genetic factors.

It's important to note that many of these factors can have complex and sometimes inconsistent effects on TSH levels. If you have concerns about your thyroid function, or suspect you have other genetic or health conditions affecting your thyroid levels, it's best to consult a healthcare professional for personalised advice and testing. Even if your TSH levels are normal, it is still recommended to have them checked every 6 to 12 months, as advised by your doctor.  Request an appointment with our specialists at Thomson Medical today.

Importance of TSH testing

TSH testing is considered a useful initial screening tool for evaluating thyroid function.  It helps with the below:

1. Initial thyroid function evaluation to screen for thyroid disorders before symptoms appear.

2. Diagnosing hyperthyroidism and hypothyroidism.

3. Evaluating thyroid nodules and goiters.

4. Monitoring treatment response in thyroid conditions such as thyroid hormone replacement therapy.

5. Assessing thyroid function during pregnancy.

6. Newborn screening for congenital hypothyroidism.

When should I get a TSH test?

Your doctor will usually request this thyroid test if you show symptoms of a thyroid disorder like hypothyroidism or hyperthyroidism. This test may also be requested to monitor the effectiveness of treatment when a patient is being treated for a known thyroid disorder. The blood test may be requested with other thyroid hormone tests and after a physical examination of your thyroid. TSH screening is also routinely performed in newborns.

When thyroid disorders remain untreated, they can lead to additional health complications. Thus, a TSH blood test is usually the first course of action should you experience symptoms related to thyroid issues.

How do you test TSH levels?

Your healthcare providers will usually test your TSH levels by conducting a blood test to measure these hormones.

1. Your healthcare provider will take a blood sample from a vein in your arm.

2. The collected blood sample will be sent to the laboratory for testing.

There is usually no need to do anything to prepare for the TSH blood test, such as fasting, unless your doctor is checking the blood for other issues outside of thyroid hormone levels. It is best to discuss with your healthcare provider the best ways to prepare for your TSH test beforehand.

Interpreting TSH results

Normal TSH levels typically fall between 0.4 and 4.0 milliunits per litre (mU/L). However, it's important to note that TSH levels can vary based on factors such as age, sex, and individual set points.

• Low TSH levels may suggest hyperthyroidism.

• High TSH levels may indicate hypothyroidism.

What happens when my TSH levels are too low?

Low levels of TSH signals to your body to produce less thyroid hormones as large amounts of thyroid hormones are already in your blood. If you have low levels of TSH, it means that your thyroid gland is most likely making excess thyroid hormones. This condition is called hyperthyroidism, or an overactive thyroid. Since thyroid hormones suppress TSH release, it can cause lower-than-normal TSH levels.

What are the symptoms of an overactive thyroid?

Symptoms of an overactive thyroid (hyperthyroidism) include:

1. Nervousness, anxiety and irritability.

2. Mood swings.

3. Insomnia.

4. Persistent tiredness and weakness.

5. Heat insensitivity.

6. Swelling in your neck from an enlarged thyroid gland (goitre).

7. Irregular or rapid heartbeats (palpitations).

8. Breathlessness.

9. Weight loss.

You may need to start taking thyroid hormone medications, such as antithyroid medications, to help treat your hyperthyroidism. Antithyroid drugs reduce thyroid hormone levels by blocking the synthesis and secretion of the thyroid hormone. They may also help control the disease by indirectly affecting the immune system. You'll usually need to take antithyroid medication for 12 to 18 months. Symptoms usually begin to improve within several weeks to months. After that, the dose may be slowly decreased or stopped.

What happens when TSH levels are too high?

If your TSH levels are too high, it indicates that your thyroid is not making enough thyroid hormones, leading to an underactive thyroid or hypothyroidism. Since the thyroid hormone suppresses TSH release, if you have too little thyroid hormones, it can cause your pituitary gland to make excess TSH.

What are symptoms of an underactive thyroid?

Symptoms of an underactive thyroid (hypothyroidism) include:

1. Fatigue and tiredness.

2. Weight gain.

3. Cold intolerance.

4. Constipation.

5. Dry skin and hair.

6. Muscle weakness and joint pains.

7. Slowed heart rate.

8. Heavy or irregular menstrual periods.

9. Hoarse voice.

10. Puffy face.

11. Hair loss or thinning.

12. Brittle nails.

In more advanced cases, additional symptoms may include:

• Decreased taste and smell

• Slow speech

• Low body temperature

Thyroid hormone medications are also used to cure hypothyroidism. Hypothyroidism is usually treated by taking daily hormone replacement tablets called levothyroxine. Levothyroxine replaces the thyroxine hormone, which your thyroid does not make enough of. You'll initially have regular blood tests until the correct dose of levothyroxine is reached.

It's important to note that these symptoms can vary from person to person and may develop gradually over several years. If you experience any persistent symptoms, please consult a healthcare professional for proper diagnosis and treatment.

TSH testing remains a critical tool in thyroid health assessment. As testing methodologies continue to advance, the accuracy and efficiency of TSH measurement improve, leading to better clinical outcomes for patients with thyroid disorders. Regular TSH testing, as part of a comprehensive thyroid panel, can help healthcare providers effectively diagnose, treat, and monitor thyroid conditions, ensuring optimal thyroid function and overall health.

FAQ

What can a TSH test tell you?

A TSH test is used to find out how well your thyroid is working. It can tell if you have hyperthyroidism (too much thyroid hormone) or hypothyroidism (too little thyroid hormone) in your blood. 

What is a normal level for TSH?

TSH normal values are 0.5 to 5.0 mIU/L.

Do you need to fast before a TSH test?

There are no official guidelines stating that fasting is required for a thyroid test, but if you're having other blood work done alongside thyroid blood tests, it may be part of your general blood test preparation. Be sure to ask a healthcare professional for any special instructions before your thyroid testing.

What happens when TSH is high?

Thyroid-stimulating hormone (TSH) triggers your thyroid to release its hormones, which mainly impact your body's metabolism. High TSH levels usually indicate hypothyroidism, and low TSH levels usually indicate hyperthyroidism.

What is an alarming TSH level?

Some say that TSH levels of over 2.5 milliunits per litre (mU/L) are abnormal, while others still consider that to be normal. Higher TSH levels are higher in older people, so doctors have raised the limits for older age groups. In middle age, for instance, a level of 4 mU/l is considered to be high.

Should I be concerned if my TSH levels are abnormal?

If your TSH test results are abnormal, it doesn't always mean you have a medical condition. Your healthcare provider will consider many factors when interpreting your TSH test results and will advise you accordingly based on your individual situation.

Can lack of sleep affect thyroid levels?

Indeed, acute sleep deprivation has been shown to have comparable effects on TSH and thyroid hormone concentrations in both men and women.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice, please consult a specialist at Thomson Medical. Request an appointment with Thomson Medical today.