Häromdagen kom ett mail från Izabella Wentz, PharmD, FASCP. Jag prenumererar på hennes nyhetsbrev. Det senaste handlar om tidpunkten för blodprover och det tycker jag att du också borde läsa:
Om man bara tar hormonet T4:
T4 has a five to nine day long half-life, which means that once you have become stable on it, it will take as many as 9 days for 50% of the dose to clear the body. T4 has a slow and steady release and won’t produce many peaks or valleys that can make a person feel like they are on a thyroid rollercoaster.
Whether you take T4 right before your lab tests, or haven’t taken it for up to 48 hours, your TSH value should be the same. Thus, you will get an accurate representation of your TSH value whether or not you take your T4 medication before a lab test.
Same goes for free T3 levels when you take a T4 medication. The free T3 level will also be relatively constant. Levels of free T4, however, will show a peak 2 hours after your T4 medication is given.
Om man tar kombinationsbehandling:
If you’re taking a combination medication that contains T3, like Armour, Nature-Throid, WP thyroid, compounded T4/T3 or the medication Cytomel (liothyronine), the timing of your tests really does matter, and may make a huge difference in getting you on an appropriate medication dose. This is because T3 has a half-life of only 18 hours to 3 days, depending on the person. In some, that’s less than a day for it to start rapidly declining in your body. The T3 levels thus fluctuate in the body throughout the day, and the goal is to have levels within the normal limit for most of the day.
Thus, it is usually best to postpone your combination medication until after you get your lab test done. I recommend getting your thyroid function tests done first thing in the morning, bringing your medications with you, and taking them right after you have your thyroid function tests to ensure that you get accurate test results.