When to take levathyroxine for bloodwork

[wandy07]

My last bloodwork, the nurse said that it really didn't matter when I took my levathyroxine before the bloodwork, so I waited til after the blood draw, went home and took it.  It was low, and now my dosage is lower.  So, I am wondering, before my Next blood draw, does any one know when we should really take the levathyroxine to get a correct reading.  My dog is on this, too, and we have to get up in the wee hours of the morning to give him his meds before a blood test.  Is there a website to check this out?  Thanks a lot!  wandy07

[wandy07]

Thank you!  I will check that website out!  :)  Wandy07

[kitty9309]

Hi- Here is a good article explaing why it is good to take t4 meds after the blood draw if the free t4 will be tested.
The TSH and free t3 will not be affected.

http://www.thyroidmanager.org/Chapter6/Ch-6b-4.htm

"Measured levels of free and total T4 are influenced by the interval between tablet ingestion and blood sampling. In athyreotic subjects who took 0.15-0.2 mg T4 orally, the serum free and total T4 concentrations were increased by about 20% one to four hours later, with return to baseline about nine hours after T4 ingestion; serum TSH and T3 levels showed no time-dependent variation (171)"

Hope this helps!

Kitty