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Thyroid UK
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Hypothyroid blood test

How many weeks after starting to take eltroxin , can we take blood test to test the ft3 ft4 and tsh values...( Now am on my 5th week taking eltroxin) ?? And while taking blood test in the morning , should I take eltroxin and then take blood test ?? Or without taking eltroxin should I take blood test ? Am confused.. each one saying different things.. v should nd v should not.. pls help !

4 Replies

You need to leave at least six weeks before retesting.

Have the blood draw early in the morning - before 9 am - after fasting over-night.

Leave a 24 hour gap between your last dose of eltroxin and the blood draw. That way, you get the highest TSH and the lowest FT4 - which is what you need if you want an increase in dose.

Always have your blood tests done under the same circumstances so that you can compare results.

1 like

Thank u so much 😊


You're welcome. :)


So have you had blood retested yet?

Dose needs increasing in 25mcg steps until TSH around one and FT4 towards top of range and FT3 at least half way in range

All thyroid tests should be done as early as possible in morning and fasting and don't take Levo in the 24 hours prior to test, delay and take straight after. This gives highest TSH, lowest FT4 and most consistent results


TSH, FT4 and FT3, plus thyroid antibodies

Vitamin D, folate, ferritin and B12 too ideally

Put results and ranges on a new post and members can advise


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