Advice on blood test

[spidernose]

My blood test has arrived today. Was going to do it in the morning before work at around 7.30am. However I last at around 9.30pm. Is this OK or should I leave it until Thursday morning and ensure I eat earlier tomorrow night?

[Clutter]

Spidernose,

7.30am tomorrow will be fine.

[shaws]

You can do it early tomorrow morning. The earlier the better as TSH is highest then. It is levothyroxine we've to allow approx 24 hours between dose and test. Your food will have digested well before tomorrow morning.

[StitchFairy]

The important thing is to make sure you don't take your thyroid medication, or have anything to eat until after the test.

[tilomilo]

Oh gosh i didn't know that, the dr never tells these things. Always take my levo about 7.30am, and blood test at 8.30 once the clinic opens :/

[RedApple in reply to tilomilo]

tilomilo, 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.