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What are T3, T4, and TSH?

Understanding your thyroid test results

With Cory Rice DO

Healthy TSH levels are usually an indicator that the whole system is working as it should.

Thyroid disorders are complicated, fickle, and highly individual — meaning thyroid issues are going to look very different for each person. In any case, it’s important to have a basic understanding of how the thyroid gland works and the hormones it produces. This understanding can help you advocate for yourself and ask the right questions when you visit your healthcare provider. It can also clue you into some of those mysterious symptoms you may be experiencing. 

An introduction to the thyroid gland

First things first: The thyroid gland is part and parcel of the endocrine system, which is a collection of glands that produce all-important hormones responsible for metabolism, growth, sexual function, sleep, and your mood. 

The gland, which is tiny and butterfly-shaped, is found at the bottom front of your neck. It makes the two main thyroid hormones, triiodothyronine (T3) and thyroxine (T4) — both of which have a major hand in your energy levels, internal temperature, hair, skin, weight, and more. For this reason, T3 and T4 are definitely not to be taken for granted — and you probably know this already if you’ve experienced any of the frustrating symptoms of a thyroid disorder. 

According to Dr. Cory Rice, DO, an internal medicine physician and certified practitioner with BioTE Medical, “When thyroid hormone levels are off, several issues can arise. You can have an overactive thyroid gland where too much thyroid hormone is produced (Hyperthyroidism). An example of this is Grave’s disease. You can also have an underactive thyroid gland in which too little thyroid hormone is produced (Hypothyroidism). An example of this is Hashimoto's thyroiditis.”

Understanding the two main thyroid hormones: T3 & T4

The thyroid gland takes its direction from both the hypothalamus (which is in your brain) and the pituitary gland, a pea-sized gland at the base of your skull. In a complex dance, the hypothalamus releases something called thyrotropin-releasing hormone, which then triggers the pituitary gland to produce something called the thyroid stimulating hormone (TSH). The TSH is then what helps your thyroid gland release T4 and T3. Without TSH, the system would fail.

Thyroxine (T4) is responsible for your metabolism, mood, and body temperature, among other things. T3, too, is made in the thyroid gland, and it can also be made in other tissues within the body by converting T4 (in a process called deiodination) into T3. This hormone is at the center of your digestive and metabolic function, and it also oversees bone health. 

So, if your T3 and T4 levels are too low, the pituitary gland will release more TSH. If they’re too high, the gland will release less TSH — but this give and take system only works if everything is functioning properly.

When you have too much T3 or T4, you might experience:

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

When you specifically have too much T3, you might experience thyrotoxicosis, a condition that comes from an overactive thyroid gland, or hyperthyroidism.

It’s also important to note that hormone levels are very complex. For example, an elevated free T4 —along with a low TSH — could indicate hyperthyroidism. 

When you have too little T3 or T4, you might experience:

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

Understanding thyroid stimulating hormone (TSH)

As mentioned above, the thyroid stimulating hormone (aka thyrotropin or thyrotrophin) is produced by the pituitary gland. It works sort of like the master of the hormones, and rules the production of T3 and T4 from its control center.

If you have too much TSH, it might mean that your thyroid gland isn’t making enough T3 or T4. Remember, the TSH is supposed to stimulate the thyroid gland — but if the gland isn’t responding, then you’ll have too much TSH in your system.

If your TSH levels are too low, it may mean that your thyroid gland is making too much thyroid hormone. This excessive thyroid production could actually suppress the TSH.

A word of warning for pregnant women: It’s incredibly important that your hormones are balanced in pregnancy, as thyroid stimulating hormone plays a role in the development of a healthy fetus.

Testing your thyroid levels

According to the American Thyroid Association, there isn’t one test for every situation; in fact, there are several kinds of thyroid tests. But if you are concerned about thyroid issues, or if your hormones are imbalanced, your doctor may provide an initial TSH level blood test. This is because the TSH level can serve as a tip-off to other, more specific issues.

What’s a normal TSH level? “Most lab companies have a wide reference as it relates to TSH levels (0.4-4.0 mIU/L),” Dr. Rice says. So, if your results are somewhere between 0.4-4.0, you’d be in the “normal” range. However, there is research that suggests that the reference range for TSH should be narrowed to 0.4 to 2.5, says Dr. Rice, which means that the “normal range” could be even smaller than some healthcare providers might think.

Generally, healthy TSH levels are an indicator the whole system is working well, but that’s an oversimplification at best. A normal T3 level might be somewhere between 100 to 200 nanograms per deciliter (ng/dL), while a normal T4 level falls between 5.0 to 12.0 micrograms per deciliter (μg/dL). Free T4, which tests for the amount of T4 that is available in the body, should range between 0.8 to 1.8 nanograms per deciliter (ng/dL).

However, it’s important to note that different labs and doctors may have a varying “normal range.” There also isn’t one single laboratory test that can tell you exactly what might be going wrong, or that is totally accurate in diagnosis, which is why you may need a few different tests. Furthermore, you may need a thyroid ultrasound or biopsy to determine the exact cause of your symptoms or hormone level imbalance. There are several different thyroid disorders — all with their own root causes. Your endocrinologist or thyroid specialist will know what to test for, as there are many different tests per your specific condition and levels.

Questions to ask your endocrinologist:

  • What tests do I need to check my thyroid levels?
  • What are the normal ranges for each hormone?
  • Are my T3, T4, and TSH levels normal?
  • Are my symptoms indicative of a thyroid disorder?
  • How can we correct any issues with the levels through medication or lifestyle changes?
  • Are there any side effects to the medications?
  • How long does it take before the medicine starts to work? 

Supporting a healthy thyroid

Now that you have a basic overview of thyroid function, you may be wondering if there are ways to support your thyroid health — in addition to medication. This is important because sometimes it can take a while before medication can correct hormone imbalance. In this case, the next best thing you can do is adjust your lifestyle habits.

Managing stress: Because there is a relationship between your adrenal health and your thyroid health, it’s wise to get a hold on your stress levels. When you are chronically stressed, adrenal fatigue — an overtaxing of the adrenal system — may kick in, triggering your body to release hormones as a way of coping. This chronic stress can worsen thyroid issues, leading to imbalanced hormone levels. Chronically stressed? You might notice slowed metabolism and weight gain — and stress may even further lower your levels of T3 and T4. It can also affect the conversion of T4 into T3.

For this reason, it’s key to find a regular stress management ritual. This might be a daily yoga, meditation, or journaling break in which you disconnect from all distractions and stressors and simply focus on your breath and your emotional well-being. Regular nature walks — also referred to as earthing or forest bathing — have been proven to provide stress reduction on a physiological level as well. 

Eating well: There isn’t one single “thyroid diet,” but there are foods that can help support our overall health. Focus on eating nutritious, colorful, whole foods. These should include fruits, veggies, fatty fish, beans, whole grains, and lean proteins. Stock up on healthy fats, such as avocados and olive oil. Reach for rich-in-fiber foods such as carrots, lentils, and bananas.

Avoid foods that are nonnutritious or full of empty calories; these will only further any feelings of fatigue or lethargy caused by thyroid issues. Skip and reduce processed foods (anything in a bag or box), candies, sodas, and junk foods. When it comes to supplementation, beware of products that contain hidden T3, which can increase your levels. Be sure to speak with your doctor before taking any supplements.

Movement is important: Exercise is critical — but it’s important to clear any exercise with your doctor. This is because hyperthyroid patients (who already have a revved-up metabolism) may experience heart issues if they excessively exercise. On the flipside, patients with hypothyroidism may want to wait until their medication has controlled their thryoid levels before kicking off a new workout routine.

That said, exercise is important — especially for hypothyroid patients, whose metabolisms have slowed down. One study published in the Archives of Medicine and Health Science, found that hypothyroid patients “should do regular physical exercise along with thyroxine replacement to improve thyroid function.” Look into lower-impact workouts, such as daily walking, hiking, swimming, or strength training.

In the end, you should work closely with your doctor to monitor your thyroid hormone levels. It may take some time and medication adjustment to find what works for you — but it’s important that you do.