In this article, we'll discuss:
- the various tests available for detecting hypothyroidism,
- what results constitute normal or thyroid function
- and what each of these tests actually looks for.
The first test is the granddaddy of the thyroid tests. Currently, it's the most common test to determine thyroid function. There are many doctors who won't test anything else. (Well, not without a little coaxing, anyway!)
TSH, or thyroid stimulating hormone, is a product of the pituitary gland. When thyroid hormones are low, the TSH tells the thyroid to produce more. I get confused with this test because it seems to work counter-intuitively.
Remember: If TSH is too high, then you are probably hypothyroid. If TSH is too low, then you are probably hyperthyroid.
Now, that begs the question, so, what's a normal TSH level?
That can vary from lab to lab. Most endocrinologists believe that a normal TSH lies within the 0.3 to 3.0 level. (Prior to 2003, it was 0.5 to 5.5.) That may be a little factoid your doctor doesn't even know.
It may be a good idea for you to ask your doctor what the lab or clinic he or she uses determines as low or high TSH levels prior to receiving your results. It could make a difference in your diagnosis, or lack thereof.
The next test is T4, which stands for thyroxine. Thyroxine is one of the hormones produced by the thyroid itself. It gets released into the bloodstream and helps control the body's metabolism by converting oxygen and calories into energy. Most of the T4 in the blood is bound to proteins, usually called TBGs, or thyroxine binding globulins. The remainder of T4 (usually about 1 - 4% in total) acts on the body's cells.
The T4 test measures the amount of T4 hormone in the blood. There are two types of T4 tests. One is the Total T4, or Serum Thyroxine.
Just as its name suggests, this test measures the total amount of thyroxine in the blood. Lower than normal levels of thyroxine along with an elevated TSH indicate hypothyroidism. The range is generally between 4.5 - 12.5.
The second T4 test is called Free T4. It refers to that 1 - 4% of T4 that does not bind with the TBGs. A result of less than 0.7 can indicate potential hypothyroidism.
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