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Can I undergo thyroid function test while on levothyroxine medication?

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Internal Medicine Specialist
Practicing since : 1980
Answered : 1357 Questions
I have been on levothyroxine for years. My new doctor wants to run a thyroid function test. I ran out of pills on December16 and now would like to just make sure I have them completely out of my system before I have the test. It has been forever since i had It evaluated. How long should I wait? I don't want a partially right test.
Posted Sun, 26 Jan 2014 in Thyroid Problem and Hormonal Problems
Answered by Dr. Rakesh Karanwal 31 minutes later
Brief Answer: Get Thyroid Function Test done AT THE EARLIEST Detailed Answer: Hi there, Thanks for your query. Since you have been on Levothyroxine for years, I presume that you are suffering from Auto-immune Hypothyroidism, a condition which requires LIFELONG Levothyroxine. THE DRUG IS SUPPOSED TO TAKEN "WITHOUT BREAK" LIFELONG. The standard principle of treatment is to titrate the dose of Levothyroxine, so as to maintain TSH levels to around 1 Hence, once TSH level has been stabilized to the desired level, Thyroid function test is performed at least ONCE in six-months. Stoppage of Levothyroxine will REVERT YOUR CONDITION BACK TO SQUARE ONE. I would therefore STRONGLY RECOMMEND that- instead of waiting for thyroid hormone "to get flushed out completely from the system"- get your Thyroid function test done AT THE EARLIEST. Your doctor will once again have to start all over again from scratch and adjust the dose of Levothyroxine till the target level of TSH is maintained. PLEASE REMEMBER : DO NOT stop Levothyroxine all-together in future. Consult your doctor and apprise him of my opinion. I am certain that he will agree with my opinion; order required tests, and- based on the reports- will arrive at a certain diagnosis and prescribe suitable treatment as advised. Hope I have addressed to your concerns to your complete satisfaction and you find my response helpful and informative. I will be happy to answer further queries, if any. Fond regards and have a nice day, Col (Dr.) Rakesh Karanwal
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Follow-up: Can I undergo thyroid function test while on levothyroxine medication? 5 hours later
Thank you for your advice. Can you please also answer my question which was how long the medication takes to leave my system. I will follow up with my doctor.
Answered by Dr. Rakesh Karanwal 13 minutes later
Brief Answer: Levothyroxine gets flushed out in 2-3 days' time Detailed Answer: The daily dose Levothyroxine is completely utilized in the next 24 hours (before the next dose is due the following day) and therefore, does NOT remain in the system. There may, however, be a minimal residual amount of drug in the blood, which too gets completely utilized within 24-48 hours of stopping Levothyroxine. Hence, the medication gets completely flushed out from the body within a maximum of 2-3 days' time. Take care, Dr. Rakesh Karanwal
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