Thyroid Testing

Your doctor may have told you that labs are needed to assess your thyroid’s health. On the lab request form, you may notice a jumble of letters and numbers that you don’t understand. What do these all mean, and what is your doctor looking for specifically? If you are going to give blood, you really should know why.

Here is a brief explanation of what each thyroid test measures, why they need to be checked and what the ranges are to ensure your thyroid is functioning optimally.

TSH – Thyroid Stimulating Hormone

The hypothalamus is responsible for regulating automatic triggers for things like hunger, thirst, sleep, hormones and body temperature. It also monitors the level of thyroid hormones in your bloodstream. If it finds that your levels are lower than needed, it will send out a Thyroid Releasing Hormone, (TRH) to the pituitary gland. Then the pituitary gland releases the Thyroid Stimulating Hormone (TSH) that produces more thyroid hormones (T4’s).

  • If it’s too high, you may not be producing enough thyroid hormones. This would make you hypothyroid
  • If it’s too low, you are over-producing thyroid hormones and are hyperthyroid.
  • If the TSH levels fall within the normal range, you may not have thyroid dysfunction, but normal does not always mean optimal.


T4 Hormone

The T4 is circulated throughout the bloodstream and is stored in tissues so that it’s available when needed.

  • If it’s too high, it indicates an overactive thyroid or hyperthyroidism
  • If it’s too low, it indicates an underactive thyroid or hypothyroidism


Free T3 Hormone

Your body converts stored T4 hormones into Free T3, which is the active form of the hormone. These hormones attach to receptors inside of your cells to power your metabolic processes.

  • If it’s too high, your thyroid is overactive or hyperthyroidism
  • If it’s too low, you aren’t converting T4 to FT3 properly and probably are hypothyroid. It’s the most common causes of low thyroid or hypothyroidism.


Reverse T3 Hormone

Your body uses some of of the T4 to create Reverse T3 (RT3), an inactive form of thyroid hormone. It is needed to slow down your metabolic processes.

  • If it’s too high, you are converting too much T4 to RT3 and not enough to FT3, which can cause hypothyroid symptoms.

It’s important to know your thyroid condition to determine if you have an autoimmune disease. This disease can be treated and reversed by targeting underlying causes like leaky gut, toxicity, infections and stress.


The Thyroid antibody


The Thyroid peroxidase antibody (TPO) is the most common test for autoimmune thyroid disease. It detects Graves’ disease or Hashimoto thyroiditis. If your antibodies are elevated your immune system is attacking your thyroid and you have autoimmune thyroid disease.

Women are more likely than men to have low thyroid hormone levels. Many people with hypothyroidism or subclinical hypothyroidism aren’t aware anything is wrong because they haven’t been tested.

Thyroid blood tests are generally straightforward and accurate, but there are some factors that can affect your results.

  • Fasting – Studies show thyroid blood tests taken after overnight fasting translate to higher TSH levels compared to those taken later in the day with no fasting. A diagnosis of hypothyroidism may be missed if you get your blood test when your TSH value is at its lowest of the day due to a non-fasting afternoon blood draw.
  • Lifestyle – Stress, lack of sleep, dieting, and different times of the menstrual cycle may impact thyroid test results.
  • Medications – Certain medications can cause thyroid dysfunction by interfering with the body’s thyroid hormone levels.
  • Pregnancy – Thyroid hormone levels change during pregnancy. In fact, the normal reference ranges can change throughout pregnancy.


It’s important to follow your doctors’ instructions and to be consistent about your thyroid tests to get the most accurate results.

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