Hypothyroidism, Basal Body Temperature and Thyroid Lab Tests

This is a very lengthy post, but I think important for everyone to know, because our main stream doctors are not doing enough. This is a prime example of the need to take our health in our own hands.

Thyroid Basics:  The thyroid gland is the main metabolism gland in our body and located in the front of the neck below the voice box. It is just about the same size and shape – and is in the same location – as a small bow tie. The thyroid secretes two hormones that are crucial for regulating metabolism: thyroxine (T4) and small amounts of triiodothyronine (T3). The numbers refer to the numbers of iodine atoms each molecule of hormone contains..
Hypothyroidism refers to a low level of thyroid hormone or underactive thyroid. It is a common problem, affecting perhaps one out of five women and a smaller percentage of men. Many functional/integrative practitioners believe that number to be much higher – as much as 40-50%! If your thyroid activity is reduced, your body may not respond as well as it should to nutritional or supplemental strategies. For that reason, a crucial step in attaining or maintaining good health is to make sure your thyroid is working properly.
Thyroid hormone and Vitamin D are the only 2 substances that every single cell in our body has receptor sites for. Since thyroid hormones affect every cell of the body, a deficiency can result in a large number of signs and symptoms (but it may only be 2-3), including low body temperature, intolerance to cold, weight gain or an inability to lose weight, depression, lack of concentration, elevated cholesterol, triglycerides, gall stones, poor digestion, constipation, decreased digestive enzymes, hair loss, general muscle and or joint pain (i.e. fibromyalgia) and fatigue. Low thyroid can down regulate progesterone receptors, contributing to hormonal symptoms every month for some women and cause low dopamine levels, leading to loss of motivation and even depression.
Hypothyroidism almost always leads to a low basal body temperature, and this is one thing everyone can check at home.

Taking Your Basal Body Temperature

  • In my opinion it is more accurate to use either an old-fashioned mercury style or the newer non-mercury glass thermometers over a digital basal body thermometer for this test.
  • Plan to take the test first thing in the morning after you wake up, because it’s important to measure temperature after you have had adequate rest.
  • Before going to sleep, if you are not using a digital thermometer, shake down a regular thermometer to below the 95-degree (35 degrees C.) mark and place it by your bed.
  • Immediately upon waking, while still lying in bed and with minimal movement, place the thermometer in your armpit (if using a glass thermometer keep it there for a full 10 min. Hold your elbow close to your side to keep the thermometer in place.
  • Read and record the temperature and date.
  • Repeat the test for 4 mornings at the same time of day and take an average to determine results.
  • An underarm reading between 97.6 (4 C) and 98.2 degrees F (36.8 C) is normal. Readings below 97.6 (36.4 C) may indicate hypothyroidism. There are differences of opinion as to the exact temperature meanings. James Wilson, in Adrenal Fatigue says on page 237 that an oral temperature below 98.2F/36.8C or 97.2F/36.2C (underarm) in indicative of suspected hypothyroidism.
  • Oral temperatures below 98.2 (36.8 C) are indicative of hypothyroidism.
  • Underarm temperatures are considered more accurate as it will not be affected by a low grade fever that may be festering.

Note: Menstruating women must perform the test on the second, third, and fourth days of menstruation. Men and postmenopausal women can perform the test at any time.


Your underarm basal body temperature should be between 36.4 degrees and 36.7 degrees F. Low basal body temperatures are quite common and may reflect hypothyroidism.

Common signs and symptoms of hypothyroidism are:

  • Depression
  • Difficulty in losing weight
  • Dry or cracked skin
  • Headaches
  • Lethargy or fatigue
  • Menstrual problems
  • Recurrent infections
  • Sensitivity to cold
  • Low libido
  • Memory loss
  • Cold intolerance/cold hands, feet
  • Fatigue
  • Gluten sensitivity
  • Loss or thinning of hair
  • Constipation
  • High cholesterol

High basal body temperatures (above 37.0 C) are less common, but may be evidence of hyperthyroidism. Common signs and symptoms of hyperthyroidism include:

  • bulging eyeballs
  • fast pulse
  • hyperactivity, nervousness
  • inability to gain weight
  • insomnia, irritability

There’s a higher chance of mental retardation in children whose mothers have low thyroid function during pregnancy, hence a strong need to be tested BEFORE becoming pregnant.

The thyroid gland is negatively impacted by a number of external chemical influences such as chlorine, fluoride, bromide, some heavy metals and other synthetic chemicals. Many people are not aware of thyroid issues because of the stubbornness of the medical establishment in looking at TSH levels only.

There is a section in your brain called the hypothalamus that releases thyrotropin releasing hormone (TRH). It tells the pituitary gland to produce thyroid stimulating hormones (TSH), which then tells the thyroid how much hormone to produce.

The thyroid gland itself puts out a number of thyroid hormones, most of it being thyroxine, otherwise known as T4. Over ninety percent of thyroid hormone produced by the thyroid gland is T4, which is considered to be a pro-hormone because it has minimal metabolic effects on the body. Triiodothyronine (T3) is the active thyroid hormone, but only seven percent is produced by the thyroid gland. The rest has to be converted from T4.

The majority of thyroid hormones produced by the thyroid are bound to a protein (thyroid binding globulin) to transport them around the rest of the body. T4 is converted to T3 in many tissues of the body, primarily the kidney and liver, and free T3 then gets into the cells to exert its metabolic effect. Gut bacteria also plays a role in converting up to 20% of these hormones.

There are many contributing factors to a poorly functioning thyroid.

  • If the pituitary is not functioning correctly, it cannot produce adequate amounts of TSH to stimulate their thyroid. This is most often due to suppression of the pituitary by cortisol.
  • Primary hypothyroidism, is the one dysfunction doctors actually look for when testing TSH, but with the reference range for TSH being so wide, many people are missed.
  • If there is too much thyroid binding globulin (TBG), thyroid hormone would be bound and unable to get into the cell. Thyroid function may be perfect, but if it’s all bound, it can’t get into the cells. This is most commonly caused by elevated estrogen in both men and women.
  • If there is not enough TBG, there can be too much free thyroid hormone available for cells and elevated free thyroid hormone shuts down receptor sites and can therefore cause hypothyroid symptoms, despite high free thyroid hormone levels. The most common cause of this is elevated testosterone in both men and women.
  • If T4 cannot be converted to T3, there will not be enough active thyroid hormone for cells. This can be due to a number of issues including nutritional deficiencies (i.e. low selenium, zinc, B vitamins ), elevated cortisol or excessive oxidative stress and is completely missed by a TSH only test!
  • This is slightly unknown territory but up to 20% of thyroid hormone is converted to active T3 in the gut. If there are significant digestive issues, or lack of healthy gut bacteria, there may be low thyroid symptoms. Another reason for regular probiotic use!
  • If thyroid hormone cannot get into the cell there will be low thyroid symptoms despite thyroid hormone levels in the body. Receptor site defects can be caused by elevations in cortisol, homocysteine or vitamin A deficiency.
  • An autoimmune condition called Hashimoto’s causes the majority of primary hypothyroidism issues ( +75%) and should (but often doesn’t) become the focus of treatment.

Thyroid Stimulating Hormone/TSH

Beginning in the 1970’s, a TSH test is what most conventional doctors relied on as the gold standard to determine if thyroid issues exist. A very broad “normal” range is given by labs as 0.3 – 4.0 or 5.0. This so-called normal range is based on the last 1000 or so lab results without regard or evaluation of the thyroid health of the person being tested! It is not too far fetched to see that the majority of people being tested, most likely have thyroid issues. The introduction of this test led most doctors to begin treating lab tests rather than perform clinical diagnostics and listen to patient symptoms. Many do not feel their best even though they fall into the so called “normal” TSH range. Don’t be surprised if your doctor tells you that you need an anti-depressant, sleeping pills or just eat less etc.

TSH is produced and secreted by your pituitary gland as a signal to your thyroid to produce more or less of its hormones. IT IS NOT ALWAYS REFLECTIVE OF HOW EFFECTIVE T4 IS CONVERTED TO THE ACTIVE T3 HORMONE. It is really important to know if your cells are getting what they really need (Free T3).

Lab Tests

So, what lab tests should you request from your doctor if you have a low basal body temperature and or thyroid symptoms? Even if you already have a diagnosis and are currently on any thyroid prescription, I urge you to get the following tests. If you are taking a T3 medication like Synthroid, you may discover that your T3 levels are still low, in which case you (with your doctor) need to rethink treatment.

TSH – this might be the only one your doctor will say you need, but insist on more
Free T3
Reverse T3 – expect to pay about $35 for this in Ontario
Free T4
Thyroid Antibodies* – Thyroid Peroxidase Antibody (TPo) and Thyroglobulin Antibody (TgA)

* These 2 lab tests are very important to determine if you have Hashimotos. Most doctors will not order these antibody tests even if you have been diagnosed with hypothyroidism, as their treatment (Synthroid or Levothyroxine) will not change. It is entirely possible though to have a low basal body temperature with some thyroid symptoms, a “normal” thyroid panel but detectable antibody levels. This most likely means that the condition is in the beginning stages. It is important to remember that the presence of thyroid antibodies means ongoing damage to the thyroid and when this damage is significant enough, more symptoms will appear and lab tests will start showing more out of range values.

If your doctor is like mine, he/she will tell you it is not necessary to order thyroid antibody tests unless your TSH is abnormal. What I did to overcome this obstacle is, I added them on the lab requisition form myself! Yes, I know that was rather cheeky and not everyone may have the guts to do this, but it sure is easier than finding a new doctor.

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