Should I take Levo before blood test? - Thyroid UK

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Should I take Levo before blood test?


Hi all, one week on from my thyroidectomy and slowly getting better. I have a blood test in morning and wondered if I should take my thyroxine as usual in the morning or wait until after blood test. I read somewhere previously about fasting beforehand but wasn't sure about taking medication?

9 Replies

Never Take thyroid hormones before a blood test, it causes a spike and you get the wrong results

Xx. G.

I queried this a few years go with the British Thyroid Foundation, and they said to take your thyroxine as normal as it is a slow release medication and will not affect the results.

helvellaAdministrator in reply to DawnD

I have never seen any reference, anywhere, to levothyroxine in any form of "slow release", extended relase or other special form. Other than this misinformation from the BTF.

I have read numerous papers (e.g. on PubMed) which demonstrate beyond doubt that there is a peak of blood FT4 around two hours after ingestion of a dose of levothyroxine. Followed by a slow reduction over the next few hours. These papers have appeared over many years, in many countries and are pretty consistent. The size of the peak, the exact timing, and the slope of the tail vary a bit, but the basic story is identical.

Two hours does not represent slow release to me. If you take a tablet of any medicine and it keeps your blood level stable (or nearly so) for eight hours or more, then that could be called slow or extended release.

DawnD in reply to helvella

I was only stating what they told me. The only error I can see in my post was saying it was "slow release" when I should have put ‘long half-life’ (when you take a dose it stays in the body a long time) .

humanbean in reply to DawnD

I agree that Levo has a long half life. The problem with taking it before getting tested is that, as helvella said, it causes a spike in the T4 levels in the blood.

Any doctor seeing a spike of Free T4 in a blood test result, possibly even over the top of the reference range, is likely to cut the prescribed dose of Levo, which just heaps misery on patients who may well already be suffering.

I think many of us would argue that a short-lived spike in results should not determine dosage because it doesn't represent what the results are throughout most of the day.

I also wanted to mention that the British Thyroid Foundation (BTF) is not a particularly popular organisation on this forum because they stick rigidly to the guidelines produced by the British Thyroid Association (BTA). And although the standard guidelines may work for many people there are a substantial minority of people who don't get well when their doctors follow the guidelines.

People like us end up being dismissed as depressed, attention-seeking hypochondriacs who just need to pull our fingers out and take anti-depressants.

DawnD in reply to humanbean

Thank you for your reply. I'm wondering if this is why my daily thyroxine has stayed the same, although I have put a lot of weight on? Maybe next time I will not take my thyroxine before the blood test.

humanbean in reply to DawnD

Weight gain on Levo is extremely common. Doctors believe it makes everyone who takes it lose weight, and nothing people say will make them change their minds. They just think patients are greedy, lazy liars.

If you want to maximise your chances of getting an increase in your Levo dose there are various things you can do :

1) Arrange blood testing as early in the morning as possible. There is a circadian rhythm to the body's production of TSH and to get the highest result you need an early test (before 9am if at all possible).

2) Don't take Levo for 24 hours before the blood draw. If you normally take Levo in the morning, take it early the day before the test, then take it after the blood draw on the day of the test.

If you normally take Levo later in the day, skip your dose entirely the day before the blood draw, and take the skipped dose immediately after the blood draw, then take it again at your usual time.

3) Always get blood taken while fasting - no food before the test, except for water which can (and should) be drunk freely.

If you still have problems you should ask for more advice on how to help yourself feel better.

One good start would be to ask for blood tests of ferritin, folate, vitamin D, and vitamin B12. I don't know whether your doctor will agree, but get what you can, ask for copies of the blood tests including reference ranges, post the results in a new post on here, and ask for feedback.

helvellaAdministrator in reply to DawnD

In no way were you wrong to report what you were told.

I have several times seen reported use of the words "slow release" which I believe is inappopriate.

Always take meds AFTER blood draw.

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