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What Causes Low TSH Levels?
Question: my tsh is low after being on 125mcg of synthroid since having a total thyroidectomy 10 yrs. ago my dr lowered my synthroid to100mcg, repeated bloodwork and a little lower still. Now going down to 75mcg have to repeat blookwork in 6 weeks again then he said if it is still low will send me for scans. What do u think this could be?
Brief Answer:
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.
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.
Note: For more information on hormonal imbalance symptoms or unmanaged diabetes with other comorbid conditions, get back to us & Consult with an Endocrinologist. Click here to book an appointment.
Above answer was peer-reviewed by :
Dr. Chakravarthy Mazumdar
Answered by
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