Blood test

[Debdieboo]

Hi

Can I ask why you say on here that you need no Levothyroxine in your system for at least 24 hours before a blood test ?

The doctor gas never said this to me ! Would it affect how much they prescribe you ? Would there be a chance you could be given a higher dose than is required thanks

[RedApple Administrator]

Debdieboo,

Would there be a chance you could be given a higher dose than is required thanks

It is more likely that you'll be given too low a dose, rather than too high. Here is the reply I made to someone else about this issue:

No, doctors don't tell you because the vast majority actually don't know this. But if your blood is drawn soon after taking the thyroxine, then your FT4 level will be falsely elevated. There is plenty of evidence/research that shows the level of hormone peaks in the blood around two hours after ingestion.

An elevated FT4 level then leads the docotor to assume you are adequately medicated when you actually need a dose increase. Or even worse, they reduce your existing dose because your FT4 is too high.

There should be at least a twelve hour gap between taking medication and having the blood draw to ensure a fairer reading. It is good to get your test done as early as possible in the morning, as this is when TSH is at it's highest. Also, consistency of time of testing is important. By that I mean always around the same time of day. If one test is done in the early morning and another in the afternoon, the results should not be compared with each other.

[Glynisrose]

Blood tests only measure what's in the blood not what is working or not. If you take your meds before a blood test then you will get a false reading.