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How long to wait for test after single LEVOTHYROXINE.

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If someone has tried a single dose of 0.05 mg of Levothyroxine once (for the first time) out of suspicion that they have hypothyroidism, how long should they wait before taking a blood test in order to get an accurate result? I believe the normal half-life of levothyroxine is 7 days for euthyroid individuals.

Thank you,

Category: Endocrinologist

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Category: Diabetologist
 32 Doctors Online

Thanks for your query at
I understand your concern
It takes 2-4 days for drug to achieve peak blood levels if it was taken intravenously so you can check elevated blood level by taking test at that time. But if you really had hypothyroidism improvement in symptoms will be seen only after many weeks of use. You are right that in euthyroid individuals half-life is 7 days and you can see elevated blood levels during this time.
Hope it was helpful
Please feel free to discuss further

Patient replied :

In order to avoid a false "normal" result due to the one dose of 0.05 mg of levothyroxine, how many days should one wait to take the blood test?

You should wait at least 24 hours to get to see elevated levels of the hormone in your blood

Patient replied :

Hello, just to be clear, in order to see levels NOT effected by the levothyroxine use, how long should one wait to take a blood test and receive results--as if they had never taken levothyroxine. It is for the purposes of initially diagnosing hypothyroidism. Thank you.

You should wait 2 to 3 weeks after levothyroxine use for hypothyroidism test
Thank you

Dr. J Muthukrishnan
Category: Diabetologist
1. 10th Asia-Pacific Pediatric Endocrine Society  Fellows meeting, Seoul, Korea, Oct 2008
2. Eighth ICMR Course on Genetics and Genetic Counseling – Jul 2008 – SGPGI, Lucknow
3. Annual Certificate Course on Endocrinological Laboratory Techniques at National Institute of Nutrition (ICMR) Hyderabad,India, ( Aug-Sep 2006) 
Fellowship: Endocrinology, Diplomate of National Board, National Academy of Medical Sciences, New Delhi, 2008, Medwin Hospital, Hyderabad
Senior Residency: Diplomate of National Board (General Medicine), National Academy of Medical Sciences, New Delhi, 2002
Residency: MD, General Medicine, 1997-2000, Armed Forces Medical College, 2nd position in University
Medical School: MBBS, Armed Forces Medical College, 1992
Dr. J Muthukrishnan and 4 other Medical Specialists are ready to help you

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