Thyroid Lab Error

[Cocothyroid]

I've had thyroid disorder now for many years and it's been well managed.

Now I'm pregnant and getting tested every month. I had a weird experience where my tested my TSH as 4.8 (0.4-4). That raised alarm bells so I went to a private clinic to get full blood work (FT3, FT4, vitamins and minerals etc.). My TSH from that lab came back as 1.4 (which is more similar to where it has been in the past). That feels like way too big a change for two weeks? Right?

Assuming one of them is a mistake then probably the best thing for me to do is retest in a week or two. But until then I need to know if I should increase my dose or not?

My question is which result would you trust more? Is it more likely to get a false high or false low? Or is it possible that they are both correct and it really can jump that much in 2 weeks?

The fact all my other results came back optional makes me think I should trust the latest "good" TSH and stick to my old dose.

Both were tested around 9am without my morning medication or having eaten.

[SlowDragon Administrator]

Welcome to the forum

Is your hypothyroidism autoimmune

Were all tests done early morning?

so I went to a private clinic to get full blood work (FT3, FT4, vitamins and minerals etc

Please add actual results

Recommended that all thyroid blood tests early morning, ideally just before 9am, only drink water between waking and test and last dose levothyroxine 24 hours before test

This gives highest TSH, lowest FT4 and most consistent results. (Patient to patient tip)

Post all about what time of day to test

healthunlocked.com/thyroidu...

[helvella]

It is well known that many blood tests can produce "oddities". These oddities are often referred to as "test interference" - where some factor has caused the result to be incorrectly high (or low).

If a result appears wrong, one standard approach is to have it re-tested at another lab that is known to use a different assay - hopefully one that s immune to the suspected interference.

This should be done with the same blood draw - one part sent to one lab and the other part sent to a second lab.

It pretty much requires co-operation from your doctor and the phlebotomist and the labs. If the results are significantly different, then it is necessary to go further and try to identify why it has happened.

Another possibility is that the the interference is due to something else you are taking, or even due to pregnancy.

I think what I am trying to say is that until it has been shown that your TSH (and any other blood tests) really has changed that much, be careful not to assume that your TSH really has changed by that much.

The other part of my reply should emphasise that this is something that is known and does happen from time to time. But test interference really shouldn't be considered as an error. No-one has done anything incorrect.

[FallingInReverse]

What is your latest FT4? That’s the most important when it comes to studies/research about requirements during pregnancy.

And the others you mention having been tested. Obviously FT3 and the others are equally important for your health.

TSH is a good indicator, but not one to dose on.

[BB001 in reply to FallingInReverse]

I suspect that stories on fT3 haven't been done that's why fT4 is considered most important during pregnancy. FT3 is the active hormone, how can it not be important?

[FallingInReverse in reply to BB001]

The answer to your question is in the biology of pregnancy, the placenta and fetal development.

The mother’s thyroid hormones need to cross the placenta to get to the baby. The mom needs excess hormones to send over. And we know the majority of maternal thyroid hormones that are successful doing that are T4. We also know that T3 isn’t as successful doing that because T3 has a shorter half life, and when we make excess our body can counter that with Reverse T3.

That being said - there are t3-mono pregnant mothers. THAT is an area where I have not found any studies. All studies will document the how’s and why’s of excess T4 needed for fetal development in the first 5-6 weeks and through mid-gestation when the baby is able to produce their own T4. Healthy babies from T3 mono moms speak for themselves, but is an area of little clinical research.

Net net though practically, there is no question about the cellular mechanisms around how effective excess (ie, exogenous ) maternal T4 is for ensuring fetal health and development for hypothyroid pregnant moms especially in the first few weeks through mid gestation.

[Cocothyroid]

Thanks for thoughtful replies!

My tests were both taken around 9am. And I'd followed the guidance on not eating/drinking and no medication for 24hr.

I have hashimotos. Antibodies are always very high and testing positive (110 today but frequently measures off the chart)

My FT4 was 15 (9-19), FT3 was 4 (2.4-6).

I can't think of anything different I did that might have caused interference. My instinct is to stick to my original dose and retest in a couple of weeks. I think I'd have a hard time getting co-operation between my doctor and lab so might just find a third place and see what the result is there. Im feeling pretty good and baby is healthy so I don't want to disturb that.

Very interesting about the test interferences!

[helvella in reply to Cocothyroid]

Don't take it as me saying you are causing interference!

One example is anti-mouse antibodies (as one of many heterophile antibodies) which cause interference on some assays but not others.

Heterophile antibody

en.wikipedia.org/wiki/Heter...

And have a read of my blog:

helvella - Factors that interfere with thyroid tests

A summary of factors known to interfere with thyroid tests.

helvella.blogspot.com/p/hel...

[Cocothyroid]

That is so interesting helvella thank you for sharing! I take 100mg of aspirin and saw that that is the one on the list.

Ill report back if I have another test or start getting any hypo symptoms (sometimes hard to tell difference from general pregnancy)

[helvella in reply to Cocothyroid]

However, that is quite a low dose of aspirin. So I'd not expect much impact.

It is very difficult when you are in that position. Perhaps the most important lesson to draw is not to immediately panic and make changes on the basis of one test being a bit different. Think about the possibilities before acting.

[FallingInReverse]

Your FT4 at 60% is reassuring. Just keep a close watch in your FT4, making sure to increase your Levo as advised.

I have not personally read anything saying TSH “causes” issues, but the research is clear around T4. So in as much as TSH is an indicator of your FT4 that’s what you’ll want to micromanage.

You also haven’t told us how many weeks you are? It is critically important to know where you are along the journey through mid gestation.

(Caveat- I am not a doctor nor have I been hypo and pregnant but I have read extensive primary research and clinical studies. I know what I know, but of course there tons I don’t know.)

[Cocothyroid in reply to FallingInReverse]

Ok thanks that's good to know! And very reassuring!

Im 20 weeks so past the scary first trimester. All scans have come back good and generally feeling ok. I'd been on mumsnet where lots of people attribute high TSH to their miscarriages but thats like you say, probably just down to doctors using it as an indication of T4.