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What Causes Low TSH Levels?
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Thyroid
Detailed Answer:
There is a unique concept in endocrinology called 'trophic hormone lagging behind'. What this essentially means is that the TSH will take several weeks to recover and rise back into the range of normal even though lowering the synthroid dose appropriately has lowered thyroid hormone levels in the blood much earlier.
This is a common practice pearl deployed by endocrinologists worldwide while managing thyroid conditions.
So the practical relevance of this biological phenomenon is that after lowering the synthroid dose from 125 to 100, it is prudent to check free T4 along with TSH after 6 weeks. And go primarily by the free T4 at this point even though the TSH may still remain suppressed. So if the free T4 at this juncture is in the range of normal, it is absolutely vital to not change the dose further. If, however, the dose is further reduced based on the TSH which still remains low, it will invariably result in under-dosing and the TSH will eventually rise towards higher than normal.
But if the free T4 is also higher than normal at the 6 week mark in the face of a suppressed TSH, then it is fair to lower the dose from 100 to either 88 or 75 depending on the degree of free T4 elevation.
Understanding and applying this concept is key to achieving and maintaining steady and stable control of hypothyroidism for life.
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