Some GPs are not actually all that up to speed when it comes to detecting potential thyroid gland problems
I would look at this website:-
www.thyroiduk.org.uk/tuk/index.html
The blood test for thyroid problems is called a Thyroid Function Test. The most usual tests are:
TSH, TT4 AND FT4
There is a range, which is used for the tests. These vary sometimes which is why you must always ask what the range is, so that you can see where you are in the range.
TSH = THYROID STIMULATING HORMONE
This hormone comes from the pituitary to stimulate the thyroid gland into making more hormone. TSH rises when the thyroid is struggling.
The approx. reference range for this test is 0.4 to 4.5.
TT4 = TOTAL T4
Thyroid hormones bound to proteins. TT4 lowers when the thyroid is struggling.
The approx. reference range for this test is 50 to 160.
FT4 = FREE T4
Thyroid hormones not bound to proteins. FT4 lowers when the thyroid is struggling.
The approx. reference range for this test is 10 to 24
FT3 = FREE T3
T4 converts to T3 and is the only thyroid hormone actually used by the body's cells.
The approx. reference range for Free T3 is 4 to 8.3
We at Thyroid UK believe that you need to know your Free T3 level too because this will often show low if you are not converting, and high if you have blocked receptor cells. Even if you are converting, the body needs the extra T3 that a normal thyroid produces. There has been some research to show that people feel better on a mixture of Thyroxine (T4) and Triiodothyronine (T3). Effects of Thyroxine as Compared with Thyroxine plus Triiodothyronine in patients with hypothyroidism – The New England Journal of Medicine Feb.11, 99 Vol. 340. (Click here for this article).
With all of these tests, your results could be anywhere within the range and you would be classed as "normal". If you are at the very edge of the range, either at the bottom or at the top, you could be classed as "borderline". Neither you nor your doctor truly knows what your normal is, if you did not have a blood test done before you became ill. There are also particular reasons why the blood tests remain in the normal range. If you are not converting from T4 to T3 or if your cells are not taking up the T3 normally, your T4 levels and your TSH levels will still show as normal.
The Broda Barnes Foundation tell us "Dr Barnes found that the primary reason for the inaccuracy of the blood tests for thyroid function is that the thyroid hormones are not utilized in the blood, but are utilized intracellularly. Therefore a patient can have enough thyroid hormones circulating in the blood to give a "normal" reading, but if the hormones are not getting into the cells, the patient will be hypothyroid.
Also, there is a problem of low blood volume in hypothyroid patients. This means that any blood test value will appear higher than it actually is because the patient has a lower than normal blood volume. In many patients with "normal" or "high" thyroid blood levels, but many clinical symptoms, the patient's blood levels actually drop lower once the patient is given thyroid hormones simply because their blood volume increases