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

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 ...

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.

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.