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What Causes Low T3?

Posted on Mon, 28 Apr 2014

Question: What can make T3 low. Mine is 64. Was 107 last year. Had PTC removed thyroid last January. Been on synthryoid 150 mcg. Was feeling ok till about 6 wks ago now I feel like I did before surgery. TSH is normal and T4 is on the high side of normal.

Answered by Dr. Shehzad Topiwala (1 hour later)

Brief Answer: Thyroid Detailed Answer: Are you on high doses of steroids like prednisone, or on a medication called propranolol. The latter is often used for heart problems and high blood pressure, although it can be used for multiple other medical conditions. These are just 2 examples of medications that can reduce the conversion of T4 to T3 in the body. There are many others however this is not significant as long as the TSH stays within the range of normal. Because if the conversion is significantly affected then the TSH rises. Conversion of T4 to T3 is performed by the body in all cells because T3 is the main agent. You may wonder why then we give synthroid which is T4. The answer is that scientifically it is appropriate to give T4 to the body and let the body decide how much of T3 it needs from T4. Further, given your thyroid cancer history you need to keep the TSH suppressed. I suggest you follow up regularly with an endocrinologist to ensure stable target levels

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Shehzad Topiwala (15 minutes later)

I'm not on any other medications. Should I take less synthroid I'm back to being very tired and can't lose weight my TSH was .5 can the low T3 be causing the fatigue, blurred vision and hot then cold fluctuation. Is there any concerns of having low T3 I don't see my Dr till mid May

Answered by Dr. Shehzad Topiwala (22 hours later)

Brief Answer: Follow up Detailed Answer: The goal for TSH is to be keep it lower than what it is now in view of your thyroid cancer history. The dose ought to be increased but this must be done by an endocrinologist only, after in person examinations and assessments. Increasing the synthroid will automatically increase the T3 too. The latest thyroid guidelines do not even require us to check T3 levels in routine management of hypothyroidism, and replacement of T3 is not required either.

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Shehzad Topiwala (54 minutes later)

I just saw that you are an endocrinologist and you know the latest guidelines so upping my synthroid will address all the symptoms? Being my TSH is already low at .5 how much more synthroid can I take? If I don't have a thyroid anymore I can't be at much risk for cancer so I will do whatever I can to get back to feeling good again. Is there anything you might suggest I could do till I get into my Frs next month?

Answered by Dr. Shehzad Topiwala (1 hour later)

Brief Answer: Second follow up Detailed Answer: Thyroid matters are not so simple to dissect out as you are logically trying to. There is a considerable complex science that goes into our decision making. At the moment, you need to have your endocrinologist address the optimal synthroid dose for you in the context of your thyroid cancer history. Yes there is potential for an increase in the dose but I cannot recommend the precise dose on an online forum without having the opportunity to examine you thoroughly in person

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Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar