While this test certainly isn’t an official diagnosis of a thyroid disorder, it can give you some indication, so you can follow up with your doctor and advocate for further testing.
You will need a special BBT thermometer. You may already have one if you are charting your cycles.
As soon as you wake up in the morning, before you get out of bed or move around, put the thermometer between your arm and your armpit, next to the skin, and leave it for ten minutes. Record the readings for at least 5 consecutive days but 10 days is optimal. You should not test during the first 5 days of your menstrual period.
If the average BBT is below 97.4 Fahrenheit, you may have an issue with your thyroid. An average BBT between 97.8 and 98.2 is considered normal. Some practitioners say that temperatures from 97.6 to 98.0 are considered evidence of possible hypothyroidism.
The test should be part of an overall approach, and not the sole diagnostic. Holistic thyroid expert Dr. Richard Shames has said:
“For those who have already been diagnosed with hypothyroidism, the basal temperature test is an additional piece of observational measurement that helps determine whether a person is on the right medicine and/or the right dose, along with considering the response to medication, physical signs (especially ankle reflexes and skin temperature), and blood test results…Temperature testing, however, is not infallible, and — like any other test — should never be used alone to rule in or rule out a thyroid condition, or to dictate therapy. This is simply a good piece of information that should be used wisely.”