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Thyroid Stimulating Hormone (TSH) - description and reference ranges

What is it?

Thyroid Stimulating Hormone (TSH). In order for the thyroid to produce essential hormones the brain needs to tell it to do so. The responsibility for that lies with the pituitary gland, which produces Thyroid Stimulating Hormone (TSH). The TSH stimulates the thyroid to produce triiodothyronine (T3) and thyroxine (T4) hormones, which are then used to control various body networks, from metabolism to growth and weight.

The more TSH is produced the more T3/T4 is consequently produced, so the TSH is a good indicator of how well the thyroid is performing.

If there is too much T3 or T4 then the thyroid is working too hard (overactive) and producing too much T3/T4. So there is no need for extra TSH to stimulate the thyroid gland. So the TSH concentration will be lower.

If, on the other hand, the thyroid is not particularly active (underactive) and is not producing enough T3/T4 then the pituitary gland has to produce more TSH to stimulate the thyroid and hence the concentration of TSH will be higher.

Reference ranges

If your indicative TSH level is lower than the reference range for our laboratory:

For a meaningful picture TSH needs to be examined together with T3/T4. General scenarios for low TSH are as follows, but it is important to discuss these numbers with your GP, as the variation and causes is substantial.

If your TSH is low and both (or either) T3 and T4 values are withing reference range, then is may be the case that mild hyperthyroidism is at play.

If your TSH is low and both (or either) T3 and T4 are within normal reference range or higher, then hyperthyroidism is possible.

If your TSH is low and both (or either) T3 and T4 are wirhing normal reference range or lower, then most likely it is not a thyroid issue.

You should discuss this result with your GP.

If your indicative THS level is higher than the reference range for our laboratory:

For a meaningful picture TSH needs to be examined together with T3/T4. General scenarios for high TSH are as follows, but it is important to discuss these numbers with your GP, as the variation and causes is substantial.

If your TSH is high and both T3 and T4 are within the normal reference range, then it is possible that mild hypothyroidism is developing

If your TSH is high and both T3 and T4 are lower than their respective reference ranges, then hypothyroidism is possible.

You should discuss this result with your GP.

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