Basal Body Temperature

The basal body temperature is perhaps the most sensitive functional test of thyroid function. A simple method for taking your basal body temperature is detailed below.

Most estimates on the rate of hypothyroidism are based on using low levels of thyroid hormone levels in the blood. As already mentioned, this may mean a large number of people with mild hypothyroidism go undetected. None the less, using blood levels of thyroid hormones as the criteria, it is estimated that between 1% - 4% of the adult population have moderate to severe hypothyroidism, and another 10% - 12% have mild hypothyroidism. The rate of hypothyroidism increases steadily with advancing age.

Some writers of popular book using medical history, physical examination and basal body temperatures, along with the blood thyroid levels, as the diagnostic criteria estimate the rate of hypothyroidism in the diagnostic criteria estimate the rate of hypothyroidism in the general adult population to be approximately 40%. It is likely that the true rate of hypothyroidism using this criteria is somewhere near 25% of the population.

​Taking your basal body temperature:

Your body temperature reflects your metabolic rate, which is largely determined by hormones secreted by the thyroid gland. The function of the thyroid gland can be determined simply by measuring your basal body temperature. All that is needed is a thermometer.

    • Shake down the thermometer to below 95 F (35 C) and place it by your bed before going to sleep.
    • On waking place the thermometer in your armpit for a full 10 minutes. It is important to make as little movement as possible. Lying down and resting with your eyes closed is best.
    Do not get up until the 10 minute test is completed.
    • After 10 minutes, read and record the temperature and date.
    • Record the temperature for at least three mornings (preferably at the same time of day) and give the information to your physician. 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 basal body temperature should be between 97.6 F (36.4 C) and 98.2 F (36.7 C). Low basal body temperatures are quite common and may reflect hypothyroidism. High basal body temperature (above 98.6 F, 37.0 C) are less common, but may be evidence of hypothyroidism. Common signs and symptoms of hyperthyroidism include bulging eyeballs, fast pulse, hyperactivity, inability to gain weight, insomnia, irritability, menstrual problems and nervousness.