Every single cell in your body has thyroid hormones.  As a result, there can really be no single test to determine how your body is absorbing thyroid hormones. There are tests to determine whether your thyroid is working, but if you can't absorb the hormones that it produces? That's another story!!

Although there are a variety of blood tests that can be taken and read together to try and get the big picture over how your body absorbs thyroid hormones, some doctors believe that your basal body temperature is the single most important indicator to that effect.

Dr. Broda Barnes has seriously covered this in his book: Hypothyroidism: The Unsuspected Illness. I recommend this book, as it contains a lot of helpful information. There are other doctors that believe body temperature alone is the single most important predictor of hypothyroidism. Dr. Wilson and Dr. Lowe are well known for treating according to symptoms, and include the importance of body temperature.

For example, see:

Dr. Broda Barnes
Hypo-Thyroidism: The Unsuspected Illness
pg: 42-48

"The body thermostat of a thyroid-deficient person may call for more heat, but thyroid hormone is essential for the oxidation or burning of fuel in the body, and in the thyroid-deficient person body temperature falls below normal because of inadequate oxidation" pg. 42.

" I could report in 'The Journal of the American Medical Association' on a study with one thousand college students whose basal temperatures were taken and who also received basal metabolism tests. The study indicated that a subnormal body temperature is a better index of hypothyroidism and the need for thyroid treatment than the basal metabolic rate." pg. 43.

"Thus, it seemed that axillary, or underarm, terperature might serve as a simple guid to determining low thyroid function and the need for thyroid therapy . . .A temperature below 97.8 indicates hypothyroidism" pg. 46.

"When no other reason can be found, no clear-cut diagnosis made, to explain the presence of symptoms or a whole complex of symptoms, it is worthwile taking a thermometer to bed with you . . . A reading below the normal range of 97.8 to 98.2 strongly suggests low thyroid function." pg. 48.

Or, see:

Dr. Wilson
http://www.wilsonssyndrome.com/Iden...TheProblems.htm

"Under periods of stress (such as childbirth, divorce, or death of a loved one) the metabolism can slow down as a coping mechanism. That's a normal response the body uses to conserve energy. After the stress has passed, the metabolism is supposed to return to normal but sometimes it doesn't. The metabolism can remain persistently slow, as demonstrated by a low body temperature, even though the stress has passed. This condition is known as Wilson's Thyroid Syndrome (WTS) because it causes low-thyroid-like symptoms and because it often responds characteristically well to a special thyroid medicine treatment, even though thyroid blood tests are often normal (You can use the links at the top left of this page to find out more about WTS). When the metabolism slows down it can adversely affect all other bodily functions . . ."

For anyone suffering and looking for a good doctor, I highly recommend that you document your body temperature for a period of time leading up to your first visit. The more information you have, the better. For more specifics on how to prepare for that first visit, including how to use your body temperature to your advantage, see the "What To Do Now" section on my site at  http://diagnosis.4t.com/custom4.html