THYROID Stimulating Hormone-TSH


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The thyroid stimulating hormone (TSH) is produced and secreted by the pituitary gland and stimulates the thyroid to produce T3 and T4. When TSH is elevated, low thyroid function may be indicated. If TSH is low it is indicative of high thyroid function. A study found that TSH was suppressed in all subjects after food, so fasting may be suggested although it is not reqired by Quest. Free T4 and Free T4 values did not change significantly after eating.

TSH and Your Thyroid

TSH stands for thyroid-stimulating hormone. This substance is tested during a routine TSH blood work and it reveals how well your thyroid performs. As you probably know already, the thyroid is involved in hundreds of metabolic processes that affect your entire body.

You might need a TSH test to determine if your thyroid is underactive or overactive. If your thyroid gland is not performing well, you'll feel certain symptoms, and if left untreated, various complications can arise.

The thyroid stimulating hormone (TSH) is produced and secreted by the pituitary gland and stimulates the thyroid to produce T3 and T4. When TSH is elevated, low thyroid function may be indicated. If TSH is low it is indicative of high thyroid function.

A study found that TSH was suppressed in all subjects after food, so fasting may be suggested although it is not reqired by Quest. Free T4 and Free T4 values did not change significantly after eating.

Keep reading to learn more about TSH and why you should test it soon.

What Is TSH and TSH Blood Work?

As the name implies, TSH is a substance that makes your thyroid work. It is produced by the pituitary gland situated at the base of your brain. This hormone tells your thyroid gland to produce more or fewer thyroid substances, depending on the current levels in your bloodstream.

A TSH blood work is nothing but a test or collection of tests determined to see if your thyroid works correctly. Some tests might also involve your pituitary gland to find out if it's instructing your thyroid to perform correctly.

Does the Time of Day Matter When Sampling for TSH Testing?

Yes. TSH concentration follows a diurnal rhythm. Typically, the peak occurs around midnight and the nadir (~50% of the peak value) around mid-day. Population-based reference intervals are generally obtained from subjects tested in the daytime, closer to the trough than to the peak. So, when evaluating a patient’s serial TSH concentrations, differences in sample collection time should be considered.

How Variable is TSH?

TSH has moderate intraindividual variability and even more marked interindividual variability. The interindividual coefficient of variation is about 32%; consequently, there is a wide population-based reference interval for TSH. Since the intraindividual variation is considerably less, comparing a specific patient’s current TSH level with any past level may be more illuminating than comparing the patient’s current TSH level to the reference interval. A difference of 0.7 mIU/L or greater is considered significant when evaluating a patient’s serial TSH values.

What High TSH and Low TSH Levels Mean?

Your pituitary gland is a very sensitive organ that immediately detects how many thyroid hormones you have in the bloodstream. It instructs the thyroid to produce more or less of these hormones to keep a balance and maintain your health.

If you have too much TSH then this means that your thyroid is underactive, a condition also known as hypothyroidism. If you have too little TSH in your bloodstream, this means that your thyroid gland is overactive and this condition is called hyperthyroidism.

Remember that TSH instructs the thyroid to produce its own hormones. It's an inverse feedback loop mechanism that works 24/7. If your pituitary senses that the thyroid hormones are too low in the bloodstream, it tells the thyroid to make more by releasing extra TSH.

Similarly, if you have too many thyroid hormones in your body, your pituitary drastically reduces TSH production or shuts it down altogether. That's because there's no need to produce more of them, your thyroid gland is already hyperactive.

What Is the Normal TSH Range?

An optimal TSH range is defined as anything between 0.5mU/L and 4.5mU/L, although many physicians in the hormone field use 3.5mU/L as the upper limit to decide to order a more detailed comprehensive thyroid panel.  If you have very low TSH and certain symptoms explained below, you may suffer from hyperthyroidism. If you have high TSH you may have hypothyroidism and you would be a good candidate for thyroid treatment.

However, keep in mind that not everyone is built the same. Some people might still be healthy with a slightly higher TSH value while others might not. It's all about finding the sweet spot that works for you. This can be done by monitoring your blood work and frequently talking with your doctor.

For example, pregnancy is known to affect TSH levels. In this case, the TSH shouldn't be allowed to go upwards of 3mU/L because it might affect the health of the baby and mother. Similarly, aging naturally increases TSH levels and this should be considered when setting a specific TSH goal for a patient.

What Are the Symptoms of High TSH?

Remember that high TSH indicates a slow thyroid gland that doesn't produce enough hormones such as T3 and T4. Essentially, the symptoms of high TSH are common with the symptoms of hypothyroidism. Let's take a look at them.

  • Excessive fatigue, even after a good night's sleep
  • Anxiety and depression
  • Intolerance to cold
  • A heart that beats slower than normal
  • Constipation
  • Thinning of hair
  • Unexplained weight changes

As you can see, these symptoms are common to other health problems and illnesses. That's why you need to do a blood test and have it checked in a laboratory to determine if your thyroid gland is lazy or not.

Some people live with high TSH for years before they finally go to a doctor and realize they have thyroid problems. You can prevent that with a simple direct-to-consumer blood test. By doing so, you will also avoid any thyroid complications that might develop over the years.

What Are the Causes of High TSH?

Your TSH levels might be too high because they are desperately trying to bring your thyroid gland back into full action. If you have high TSH because of an underactive thyroid gland, this is called primary hypothyroidism and it's one of the most popular thyroid problems.

In this case, your doctor might prescribe medicines and lifestyle changes to make your thyroid function normally again. In other cases, some people have high levels of TSH and a normal-functioning thyroid gland.

This is usually because some antibodies are also present in the system. The patient might struggle with certain autoimmune diseases that cause the TSH levels to be too high.

If you're already receiving treatment for hypothyroidism but your TSH levels are still too high then this means that your current thyroid medicine dosage is not sufficient. You might need to talk to your doctor, do some tests, and readjust your dosage accordingly.

However, the human body is very complex and although you might receive the correct thyroid meds, your system might not absorb them properly. Other drugs or vitamin deficiencies might prevent your body from doing so.

That's why it's important to test your TSH levels and seek the counsel of your primary healthcare provider. It's necessary to narrow down all these scenarios to find exactly why your TSH levels are high and what can you do about it.

What Are the Symptoms of Low TSH?

You might have low TSH production because your thyroid gland is overactive. In this scenario, the pituitary gland minimizes TSH release or shuts it down completely. Having an overactive thyroid is known as hyperthyroidism. Here are the symptoms of low TSH.

  • Sensitivity to light, odors, and sounds
  • Excessive sweating
  • Increased blood pressure
  • Tremors in hands and feet
  • Irregular bowel movements or diarrhea
  • Excessive fatigue
  • Unexplained weight loss

These symptoms are commonly associated with confusion, mental fog, and memory problems. They can persist for a long time as thyroid problems develop. Doing a TSH test and eventually, other thyroid tests help you avoid all these symptoms and complications.

What Are the Causes of Low TSH?

People who have very low TSH levels are most likely diagnosed with some form of thyroid problem. This can be caused by autoimmune diseases such as Hashimoto's disease, lupus, and so on. In other cases, toxic nodules might be present in the thyroid gland and this is what's causing it to be overactive.

An enlarged thyroid gland (aka goiter) is also one of the causes of hyperthyroidism. In all these cases, the pituitary secretes less TSH to prevent thyroid complications. If you do a basic TSH test and your doctor sees that your TSH levels are low, it's possible that more thyroid tests need to be done.

Controversies Surrounding the Use of the TSH as the Main Way to Detect Thyroid Disease

The first signs of low thyroid function are typically related to symptoms like fatigue, weight gain, cold intolerance, hair loss, sexual dysfunction, etc. and blood screening using the Thyroid Stimulating Hormone (TSH) test with other thyroid hormone biomarkers including free thyroxine (T4, free). Unfortunately, some physicians only measure TSH as a way to diagnose low or high thyroid function. Even though some guidelines suggest a TSH range of 0.4-4.5 micro IU/mL, some patients may be experiencing hypothyroidism symptoms at TSH levels above 3 due to occult Hashimoto’s disease or other issues, so it is always a good idea to perform a thyroid panel that includes not only TSH but also free T3 and free T4. There is ongoing controversy about whether reliance on the TSH test -- to the exclusion of clinical symptoms and other tests such as Free T4, Free T3, and antibodies tests -- is medically sound. That is a controversy that is unlikely to be decided for years. The situation today, however, is that the majority of physicians do rely almost exclusively on the TSH test to detect thyroid disease, and monitor the effectiveness of treatment.

How To Prepare for a TSH Test?

Keep in mind that your pituitary gland constantly adjusts how many hormones it produces, depending on the thyroid hormones present in the bloodstream. Therefore, certain aspects can interfere with the results and you should know about them before doing the test.

For example, fasting before a test might make your TSH levels come back slightly higher. If you don't eat for a period of time, your pituitary is producing more TSH to keep the thyroid gland working. On the other hand, pregnancy almost always returns lower-than-normal TSH results. This has nothing to do with a thyroid problem, it's just pregnancy hormones causing bodily changes.

Various medications can also affect the test and it's recommended to avoid them. For example, Advil (ibuprofen) and other nonsteroidal anti-inflammatory drugs might interfere with the results. Having a poor night's sleep can also affect your TSH levels and produce slightly inaccurate results.

Many multivitamins, supplements (especially hair and nail), and over-the-counter and prescription medications may affect thyroid test results and their use should be discussed with your healthcare practitioner prior to testing. For example, biotin (vitamin B7) can interfere with some lab tests, so your healthcare practitioner may advise you to refrain from taking biotin or supplements that contain biotin for a few days before having blood drawn for a TSH test. Also, foods that are rich in iodine and kelp might have an effect on the thyroid gland and automatically alter TSH results.

Factors that Can Affect TSH Test Results

Time of Day

  1. Circadian Rhythm: TSH levels are usually higher in the early morning and lower in the afternoon.

Age and Gender

  1. Age: TSH levels tend to increase with age.
  2. Gender: Women, especially those who are pregnant or menopausal, may experience fluctuating TSH levels.

Lifestyle Factors

  1. Diet: Consuming an excessive amount of iodine or being iodine-deficient can impact TSH levels. Also, taking thyroid treatment with food or coffee can decrease absorption.
  2. Stress: Chronic stress can potentially affect the hormonal balance, including TSH levels.
  3. Exercise: Intense physical activity can transiently lower TSH levels.
  4. Supplements: Biotin, a commonly used vitamin for hair loss, can affect TSH test results since it interferes with the test assay.

Health Conditions

  1. Hashimoto's Disease: An autoimmune condition that can cause elevated TSH levels.
  2. Graves’ Disease: This condition usually results in suppressed TSH levels.
  3. Pituitary Disorders: Conditions like pituitary tumors can interfere with TSH production.


  1. Alcohol: Chronic alcohol abuse can affect TSH levels.
  2. Smoking: Nicotine can also affect thyroid function and, in turn, TSH levels.
  3. Recent Illness or Surgery: Any form of acute illness or surgery can temporarily affect TSH levels.

Lab Test Collection Instructions

Dietary supplements containing biotin may interfere in assays and may skew results to be either falsely high or falsely low. For patients receiving the recommended daily doses of biotin, draw samples at least 8 hours following the last biotin supplementation. For patients on mega-doses of biotin supplements, draw samples at least 72 hours following the last biotin supplementation.

All these safety precautions and instructions are usually communicated when you order a TSH blood test online, so you don't have to memorize them now. Once you get the results back by mail, you can compare them against reference values and see if you fit the normal TSH range or not.

Get Your TSH Blood Work Done Today!

Since your thyroid gland is producing essential hormones that keep you active and healthy, it's only natural to want it to perform at its peak. You can do that by testing your TSH levels regularly. Customers either order a simple TSH test or a Thyroid Panel that checks the thyroid hormones also.


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