Should patients with hypothyroidism hold their morning levothyroxine dose before going to the lab to check free T4/TSH?

There is literature showing small changes in both free T4 and TSH (despite steady state) in the first few hours after ingestion of L-T4. In occasional cases where TSH straddles the upper or lower range of normal, it might be important in your decision making regarding dosing.

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Do you advise your patients to hold their morning levothyroxine on the day of lab draw?

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3 Answers

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Endocrinology · University of Rochester School of Medicine and Dentistry

Answered on

There exists a lack of consensus regarding the optimal timing for thyroid blood tests in relation to levothyroxine administration. Given the 7-9 days half-life of T4 and the approximately 4-5 half-lives required for clearance from the system, the timing of levothyroxine intake doesn't significantly ...

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Endocrinology · Cape Regional Physicians Associates

Answered on

When patients take their T4 replacement (Levothyroxine or Synthroid) prior to lab draw, Free T4 goes up. I ask them to take their thyroid medication with them to the lab and take after their blood has been drawn.

I request all hormones be tested early fasting.

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Endocrinology · Central Florida Endocrine And Diabetes Consultants Pa

Answered on

Rarely do I ask for them to fast and not take pills before blood test. Usually, if someone has a TSH on the lower side and ft4 is not at least near mid range, I may ask them to take it right after the blood test. FT4 may be higher and TSH could be slightly lower if taken a couple of hours before.

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