TSH Test: What do Normal, High, and Low Levels Mean?

Your thyroid is a small, butterfly-shaped gland in front of your throat. Your thyroid is responsible for secreting several hormones that regulate many of your body’s processes. It can help regulate your body temperature, weight, muscle strength, and metabolism.

TSH stands for thyroid-stimulating hormone. Unfortunately, hormone levels are very complex. You may have an overactive thyroid gland (hyperthyroidism) or an underactive thyroid gland (hypothyroidism). Regardless, a thyroid disorder can cause many health problems in an individual.

TSH Test
TSH Test

What is a TSH test?

TSH stands for thyroid-stimulating hormone and is produced by the pituitary gland in the brain. This hormone stimulates the production of thyroxine, which regulates how quickly cells’ chemical reactions occur.

The TSH test helps determine whether hypothyroidism, hyperthyroidism, or has an average TSH level. It also determines whether a patient is subclinical or clinically overt, whether treatment is needed, and what kind of treatment will be given.

The normal TSH range is 0.5 to 5.0 mIU/L, which is considered to be the reference range. The upper limit of this range is at least one unit below the upper limit of the patient’s serum T4 reference range. In other words, if your T4 level is too high, your TSH level will be lower than average to compensate for it.

What do high and low levels mean?

A low TSH level means the patient has “subclinical hypothyroidism,” which doesn’t require treatment. A higher TSH level signifies a “clinically overt hypothyroidism,” where there is an abnormality in how your body uses iodine and uses thyroid hormones.

Symptoms of high thyroid levels and low thyroid levels

A TSH test is a blood test that measures this hormone. When your thyroid level isn’t enough, your body signals the pituitary gland to produce more TSH.

Similarly, the pituitary gland produces less TSH when your thyroid levels are incredibly high.

For example, when you have an overactive thyroid gland (hyperthyroidism), you may experience thyrotoxicosis (too much T3).

Therefore, A TSH test measures your thyroid hormone to determine if your thyroid isn’t working correctly. The thyroid-stimulating hormone (TSH) test examines thyroid hormone levels and measures thyroid function.

When your thyroid levels are high, you might experience symptoms, which may include:

  • Anxiety
  • Sweating
  • Hair loss
  • Feelings of irritation
  • Hyperactivity
  • Skipped periods
  • Tremors and shaking

When your thyroid levels are low, you might experience symptoms, which may include:

  • Weight gain
  • Memory issues
  • Lethargy
  • Fatigue
  • Constipation
  • Brain fog
  • Dry skin

Testing your thyroid levels

There are several tests for checking thyroid levels. However, your doctor may carry out an initial TSH level blood test.

This is because the TSH level can serve as the starting point and help unravel more specific issues.

TSH Levels

  1. Normal: <0.4 μIU/ml or <0.34 μIU/ml
  2. High: >4.5 μIU/ml or >3.5 μIU/ml
  3. Low: <0.1 μIU/ml or <0.06 μIU/ml

If you’ve been diagnosed with an overactive thyroid, it’s essential to understand your TSH levels. If you’re wondering what to do if your levels are too high or too low, this article has the answers!

Interpreting your TSH test

A high TSH means your thyroid is underactive (hypothyroid) and is not producing enough thyroid hormone.

A low TSH suggests your thyroid is overactive (hyperthyroid) and produces too much thyroid hormone.

However, just like most medical conditions and tests, this rule has some exceptions.

It’s also important to note that normal thyroid levels may be abnormal for you. For example, a TSH greater than 3.0 mU/l is abnormal in pregnancy.

Are there any risks to the test?

There is very little or no risk of having a blood test. You may have sharp pain or bruise at the spot where the needle was put in, but most pain will go away within minutes.

How TSH Levels Change

Before you carry out your TSH test, it is crucial to understand how your thyroid-stimulating hormone works. The test evaluates the levels of specific thyroid hormones and antibodies.

TSH levels are complex and can be very confusing. It’s no wonder many people wonder why a high TSH level can mean the thyroid gland is underactive and a low TSH level can mean you have an overactive thyroid.

Before we go further, let’s explain exactly how your thyroid gland works.

Your thyroid gland is responsible for producing your thyroid hormone.

When your thyroid glands are functioning correctly, your thyroid works hand in hand with your pituitary gland that involves several key steps:

Step 1: First, your pituitary gland evaluates the thyroid hormone level in your bloodstream.

Step 2: Your pituitary gland then releases a special messenger hormone (TSH), which stimulates the thyroid to release more thyroid hormone.

Step 3: In some abnormal cases, for example, when you’re ill, stressed, or after surgery, your thyroid may not be able to produce enough thyroid hormone. When this happens, your pituitary detects the diminished levels of thyroid hormone in your body and has more TSH, which triggers your thyroid gland to make more thyroid hormone.

This series of chain reactions is in your body’s effort to increase thyroid hormone levels and return the system to normal.

Step 4: Due to certain illnesses or taking an abnormal dose of a thyroid replacement drug, your thyroid can become overactive and start producing too much thyroid hormone in your body.

When your pituitary senses a surplus of thyroid hormone circulating in the body, it reduces TSH production.

This reduction in TSH level is your body’s attempt to return the thyroid hormone levels to normal levels.

Factors that can affect TSH levels

  1. TSH levels by sex

A recent study discovered that women are more likely to experience thyroid dysfunction than men. 1 in 8 women experiences thyroid problems at some point in their lives.

While some women experience hyperthyroidism, others may experience hypothyroidism or even both. Pregnancy and menopause are other factors that can change your TSH levels and cause thyroid problems.

Although there’s no definite difference between male and female TSH levels, most studies report higher TSH levels in women than men.

In some cases, thyroid conditions have been connected with sexual dysfunction. According to a 2019 study, men with sexual dysfunction may be at a higher risk of hypothyroidism. According to the study results, about 59–63% of men with hypothyroidism also experienced sexual dysfunction, while only 22–46% of females with hypothyroidism had sexual dysfunction.

  1. TSH levels by age

Age is also a major contributing factor that can affect TSH levels. As we age, our blood TSH levels tend to increase. In fact, according to the authors of certain research, people with TSH levels between 0.4 and 2.49 mIU/l fell from 88.8% among people aged 20–29 years to 61.5% in people 80 or older.

How to measure TSH levels

The TSH test is a simple test that involves your doctor taking a blood sample from the vein in your inner arm. After the blood collection is complete, the blood sample is sent to a medical laboratory for testing.

Usually, no special requirements are necessary if you undergo a TSH test. However, if your doctor tests your blood for more than one condition, you may need to fast or prepare another way.

Note: The doctor will provide the conditions before your test.

If your thyroid levels are abnormally high or low, your doctor may need to carry out at least one other diagnostic test to identify the underlying cause.

Treating hypothyroidism (high TSH levels)

Your doctor may prescribe certain medications to treat hypothyroidism. For example, levothyroxine can help replace the missing thyroid hormones in your system.

According to the Food and Drug Administration (FDA), you should take this medication once a day. You can take it in the morning or at least 30 minutes before eating. Your doctor will also prescribe how the drug should be used.

Your doctor may schedule a checkup and run additional blood tests every few months to monitor the progress of the hormone treatment.

Some certain meals can affect hormone medications. For instance, eating soybean flour, walnuts, dietary fiber, or cottonseed meal can affect how your body processes levothyroxine.

Treating hyperthyroidism (low TSH levels)

Your doctor may administer medication to help you manage the symptoms of hyperthyroidism.

To prevent long-term health complications, treatments for hyperthyroidism usually focus on reducing thyroid hormone levels.

For example, your doctor may prescribe beta-blockers and antithyroid medications that inhibit the production of hormones.

Another effective alternative is radioiodine therapy. This method involves taking a capsule or liquid that contains radioactive iodine-131, which kills cells that produce thyroid hormones.

Note: People who use radioiodine therapy as a treatment for hyperthyroidism may be prone to developing hypothyroidism in the future.

In severe cases of hyperthyroidism, or certain conditions like pregnancy, your doctor may suggest surgical removal of the thyroid gland.

Wrap Up

A TSH test estimates the measure of the thyroid hormone in the blood. Your doctor uses the outcomes of the test to analyze thyroid conditions like hypothyroidism and hyperthyroidism.

There is no average TSH level that works for everyone. TSH levels can change drastically depending on an individual’s age, sex, and body weight.

So the normal ranges remain questionable; however, for the vast majority, the normal range falls between 0.4 and 4.0 mU/l.

An overactive or underactive thyroid can cause medical problems that can interfere with your day-to-day life. During pregnancy, you may also notice a change in your thyroid levels.

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