Sometimes while interpreting thyroid function test we come across the result where it says that the thyroid hormones T3 & T4 are normal where as the TSH is suppressed how can this happen. So that can happen when there is a mile hyper function in the thyriod gland, so if there is a slight excess of thyroid hormone being produced TSH can become supress to a very low level, this is also because of a log linear relationship between the thyroid hormone and the TSH value. TSH is actually a hormone produced in the pituitary, thyroid hormones actually produced in the thyroid glands located in the neck. But under the influence of T4, there is a small increase of 1 unit increase in P4 that can be attained 10 unit reduction in the TSH. So that's why you can get a very sharp drop in the TSH before that before actually rises above its normal range, if you look at the range of the normal for it is between 4 nanogram per deciliter to about 12 nanograms per deciliter. So it is in the range of a few points actually even 1 or 2. Increase T4 can causes 10 point reduction in the TSH, the increase in T4 is mirrored by a corresponding 10-12 decrease or increase in TSH so that's the reason for the curious picture of T4 & T3 being normal and TSH being abnormally low. This can happen when there is a mild hypothyroidism.