A few months ago I had blood work done to test my thyroid levels and let me just say… the results were pretty wack! This lead me to do some research as to what can falsely throw off a thyroid test.

I scoured the internet, flipped through my books on thyroid health, and reached out to my Endocrinologist and her team for answers as to what might have caused this fluke. I figured this is probably a topic that would interest a lot of you so I wanted to share my findings with you my!


5 Factors That May Falsely Throw Off A Thyroid Test

Just to be clear, I’m not talking about things that accurately affect your thyroid levels like missing doses, changing brands, inconsistency in the time you take it or how long you wait before eating or taking certain medications. I’m talking about factors that falsely or temporarily throw off a thyroid test.


1. Taking your Meds too close to your blood draw

I’m breaking this one down into two categories…

  • If you’re on T4 only medication (like levothyroxine, synthroid, etc.) then your T4 levels will show a peak two hours after you take your dose. In this case, it’s best to take your dose after your blood draw or wait two hours after your dose, at least!
  • If you’re on combination T4 & T3 medication (like Armour, Nature-Throid, WP Thyroid, compounded T4/T3, or Cytomel) then it’s best to take your medication after the blood draw as well. This is because after taking T3 containing medication your TSH will be falsely suppressed for 5 hours. After the 5 hours it will begin to rise for about 8 hours until it stabilizes. Free T3 levels are also falsely elevated immediately after a dose of T3 containing medication, peaking at 4 hours.


2. Time of blood draw

Like your other hormones, thyroid hormones follow a natural rhythm; ebbing & flowing throughout the day. This makes the time of day you get your blood drawn pretty important.

TSH markers tend to be higher in the morning then they are in the afternoon or evening. A 2004 study found that TSH dropped an average of 26% in people who had their blood drawn in the later afternoon as opposed to first thing in the morning. This makes for a lot of missed hypothyroid diagnosis. Just look at some of the patients in this study….they had TSH’s above the 5 mU/L range in the morning, and by the afternoon they were down to the 3’s.


3. Being sick

Illness temporarily puts a lot of stress on your endocrine system. So if you’re battling a cold or virus it might be best to hold off on your lab work until you recover. Some, keyword being “some”, endocrinologists even recommend slightly increasing your dose of medication during a bout of illness or during the cold winter months.


4. Medications

Certain medications can falsely or temporarily throw off a thyroid test. Medications like NSAIDs, certain blood thinners, and Biotin.


5. Where you are in your menstrual cycle

Big surprise here, right? Wrong! What DOESN’T your cycle effect? Before ovulation estrogen levels spike, which can temporarily raise your TSH. They also rise slightly again right before your period, but the bigger influencer right before your period is Progesterone. Progesterone’s major spike happens right before your period which will temporarily lower your TSH.

menstrual cycle Hormone Chart



Moral of the Story

Hormones are sensitive. Being consistent with all things surrounding your blood draw will leave little wiggle room for things that can falsely throw off a thyroid test. Luckily you now know what can falsely alter your results which will save you from unwanted stress and possibly an unnecessary change in medication.

If your labs weren’t a fluke and your numbers are actually off, find out how you can get the most out of your thyroid meds so that you won’t have to keep increasing them!

Let Me Know…

Have you ever had bloodwork results that were totally crazy one minute then totally normal by the next draw?





  1. Jamie January 15, 2019 at 9:56 am - Reply

    Story of my life. This has happened with my cholesterol a few times and the doctors didn’t hesitate to HEAVILY push statins on me. Thankfully I never took them and learned what I was doing wrong to throw off my tests… and good news, it hasn’t happened since!

    • T1D Living January 15, 2019 at 10:47 am - Reply

      yass The statin push… I know that one all too well! Probably one of the most over prescribed, unnecessary drugs on the market.

  2. Carrie January 15, 2019 at 10:21 am - Reply

    Yikes! I’m realizing now that I pay no attention to whether or not I take my meds before labs… I will now tho. Thank you!

    • T1D Living January 15, 2019 at 10:48 am - Reply

      it’s wild to me that most doctors don’t mention it!

  3. Rachel S January 15, 2019 at 11:30 am - Reply

    ROFL “what doesn’t your cycle effect”! #truth it effects EEEEEVVVERYTHIIIIINNG

    • T1D Living January 17, 2019 at 1:17 pm - Reply

      hahah sure does!!

  4. Makenna Umi January 15, 2019 at 12:52 pm - Reply

    Talk about good timing. I have labs tomorrow. Thank you for this!

    • T1D Living January 17, 2019 at 1:20 pm - Reply

      of course! good luck!

  5. Bee January 15, 2019 at 1:05 pm - Reply

    YES! I always wait until after my blood draw to take my meds for this exact reason. I made the mistake of taking them before my draw a couple times and my endo wanted to change my dosage because it threw off my numbers so much. Needless to say I have since changed ENDOs. How is it that some docs don’t pay attention to the details like, “did you take your meds before your draw or not” or at the very least tell you to hold off on your meds until your blood draw is done. What is wrong with the western medical system?! wait… don’t answer that. lol

    • T1D Living January 17, 2019 at 1:20 pm - Reply

      oye vey! I agree, there is something very very wrong with our medical system.

  6. Rick Phillips January 15, 2019 at 9:34 pm - Reply

    Of course blood sugar is the main thing that happens to me. Mine goes up like a rocket ship in the morning. Psst, sure take the fasting blood sugar and then tell me it is too high.

    • T1D Living January 17, 2019 at 1:23 pm - Reply

      Mine too! I remember one time I had a great fasting, it was like 103, and I got “in trouble” with my endo for being over 100 mg/dL. Needless to say, I’ve switch endos.

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