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Does the contraceptive pill affect thyroid blood test results?

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  • 25-11-2012 9:20pm
    #1
    DitzyPoo92
    Registered Users Posts: 77 ✭✭


    I got a blood test 6 months ago for my thyroid. I was on the Marviol contraceptive pill at the time. The results came back that my levels were slightly below normal but I was asked back for another test last week and am waiting on the test results. At the time of my second blood test, I was off the contraceptive pill 3 months. So my question is: Does the contraceptive pill affect the outcome of the test results and in what ways? Just out of curiosity really because I've been kinda wondering. Also has anyone been in the position before where the contraceptive pill affected the thyroid blood results? Thanks!:)


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    #2
    RobFowl
    Moderators, Science, Health & Environment Moderators Posts: 11,667 Mod ✭✭✭✭RobFowl


    I'm not aware it significantly affects them but can't link to any evidence at the moment.
    Pregnancy does affect TFT's making them unreliable for the duration though.


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    #3
    Kurtosis
    Moderators, Science, Health & Environment Moderators Posts: 2,881 Mod ✭✭✭✭Kurtosis


    Oestrogen can affect serum T4 (thyroxine) levels. I believe it increases the concentration of serum thyroxine-binding globulin, a plasma protein or carrier of T4 in the bloodstream. When T4 is bound to this carrier it can be considered inactive.

    I know this is generally more of a concern when prescribing Eltroxin for hypothyroid women pre- and post-menopause or post-menopause with or without HRT because of the varying oestrogen levels. I am not sure whether the dose of oestrogen in the pill would be large enough to have any significant effect on T4 levels or whether any such effect would be picked up by TFTs which measure TSH most commonly.


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    #4
    El_Dangeroso
    Users Awaiting Email Confirmation Posts: 5,620 ✭✭✭El_Dangeroso


    Apparently it does increase T3 and T4 (20-40% - is that bad? or good?) but only moderately affects TSH:

    http://europepmc.org/abstract/MED/12742558/reload=0;jsessionid=S3h69Wq0JMh1Yecofkc8.10


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