If a GP suspects there is a problem with a patient's thyroid, the standard test conducted is a blood sample to measure the levels of TSH (Thyroid Stimulating Hormone) present. (To ensure an accurate Thyroid blood test, samples are best taken in the morning, and should not co-incide with other blood sampling tests that involve fasting).This will often determine if the body is producing/releasing enough TSH from the pituitary gland which tells the thyroid gland when to produce T4 and T3.
Pituatary Gland >> TSH >> Thyroid Gland >> T4/T3 >> Cells.
This test however is not 100% accurate for %100 of the patients when trying to diagnose hypothyroidism. For example, a patient's body may produce enough TSH, but have insufficient Iodine. With insufficient iodine to make the thyroid hormones (or insufficient selenium/zinc to convert the T4 hormone to T3 hormone) the patient's ability to produce T3 is compromised. The symptoms of Hypothyroidism would then persist, even if the blood test for TSH returned a ‘normal' result. There has also been debate regarding what is considered to be a ‘normal' range of TSH. The current accepted range is 0.4 - 4.0. Some health practitioners consider .4 - 2.0 to be a more normal reference range.
Higher levels of TSH indicates that the pituitary gland is producing more TSH in response the body telling it that the current levels of T4 and T3 aren't enough. Consistent readings at the upper limit of the range are not a good sign.
Asking your Doctor for a TSH, T4 and T3 test would help give a clearer picture. Some Doctors are reluctant to perform all 3 tests, trusting in the TSH test to diagnose possible hypothyroidism. However, as already stated, this test alone can still miss hypothyroid cases - especially if the common symptoms persist (cold extremities, fatigue, low mood) but treatment for these symptoms (i.e. iron supplementation, anti-depressants) have limited or no success. Note - If there is any history of autoimmune disease, a test for Thyroid anti-bodies can also be useful in determining thyroid functionality.
A traditional test (used some 50 years ago by health practitioners before blood tests were developed for hypothyroidism) which still gives accurate results is the basal temperature test.
It is free and quite simple. Since the thyroid gland controls your metabolic rate and therefore your body temperature, measuring your temperature is a accurate indication of thyroid health/function. It is important to note the body temperature must be carefully/accurately measured.
The most accurate way to measure body temperature is to:
a) Use a mercury thermometer.
b) Check the temperature upon waking (do not move before taking your temperature) - keep the thermometer by the bed and put under the arm for 10 minutes. Sometimes if measured from the mouth (instead of under the arm), a bacterial infection may raise the temperature of the mouth and return a false reading.
c) Avoid alcohol the night before you plan to take your temperature (as alcohol can raise your temperature).
d) For women, days 2-5 of the menstrual cycle gives the most accurate time to measure.
e) For all other people (young female/old female or male), any time of the month is acceptable.
f) Chart the results for at least 4 days, preferably 7 days.
g) The bodies resting temperature is 36.5C. If the results are consistently below this temperature (i.e. 36.3 or less) then this indicates a potential under active thyroid.