Different lab results on Same dose. Conflicting free assays.

[Meanbeannyc]

I want to start out by saying greygoose has been very helpful to me and without her, I probably wouldn’t be posting this... and have added a small dose of cytomel to my current T4 dose as per her advice..

But can anyone give some insight as to why my free T3 is out of range at one lab and in range at another? Looking for some opinions..

All the following labs are on Synthroid 112 DAW only.

112 Synthroid DAW...

First lab:

FT4 : 1.74 (0.78-2.19)

FT3: 2.56 (2.77-5.27)

TSH 0.47 (0.47-4.68)

Second lab:

FT4: 1.6 (0.8-1.8)

FT3: 2.6 (2.3-4.2)

TSH: 1.23 (unknown ranges).

UPDATE:

New labs at second lab: 112 synthroid DAW.

FT4: 1.4 (0.8-1.8)

FT3: 3.0 (2.3-4.2)

TSH: 0.23 (0.40-4.0)

[JAmanda]

I don't know the answer but I kind of expect tests to vary by a small degree for multiple reasons. That said, your T3 his low on both so hopefully you'll feel better once that comes up.

[Meanbeannyc in reply to JAmanda]

I’m not banking on anything yet.

[tattybogle]

The span of the range on one test is 2.5, and on the other is 1.9. So quite a bit narrower, therefore the difference in the 'result' numbers will be will be smaller for the test with the narrower range. i can't explain what i mean very well , but that will make a difference when it comes to how far under or over range a result appears to be in % terms.

As far as i understand the process for measuring fT4/3 (which is not very far at all )...

There is an element of estimation involved to get the result, and there is also an element of variation allowed. So a slightly different result on two tests , even if done from the same blood draw ,and measured on the same test machine, is to be expected. Which is not the same as it being 'wrong' , it's just the best they can do given the technical difficulties of what they are trying to isolate and measure from the blood.

From looking in detail at many results on here over the last year , i have been keeping an eye out for examples of the amount of variation between two tests when done from the same blood draw, and there is always a slight difference.

So i now look at blood test results as an indication of levels being:-

Very below range

Around the bottom of the range

Low in range

Mid range

Around the top of the range

Very over range

And i don't worry about any differences as long as they are within these boundaries.

I'd be very happy for someone who understands more about the actual science processes in labs to correct my thinking, but for now that's the best i've got

I do know it's not the same as measuring something with a ruler , where it is always possible to get a 'correct' result as long as the intervals on the ruler used are small enough.

[Meanbeannyc in reply to tattybogle]

I agree. But...

One lab says below, and the other one says low normal.

[tattybogle in reply to Meanbeannyc]

The difference in the TSH is bigger than i'd expect, as i thought that was easier technically to measure 'accurately'.

were both tests from the same blood draw ? or is there a time of day difference

[Meanbeannyc in reply to tattybogle]

Two different blood draws. Both fasted. Both same time of day. One no levo, one was unexpected and I took the levo.

[tattybogle in reply to Meanbeannyc]

Mmm ... just confirms my growing opinion that blood tests are a bit of a game of dice , and if we were tested more frequently than we are the variations in results would put paid to the "TSH tells us all we need to know " school of thought. On one set of that TSH you'd have a doctor squarking about you being overmedicated, and on the other which was presumably only a few days apart they'd be perfectly happy.

And as for the in range /under range fT3's,..... the differing range with one being so much narrower than the other, and the same problem with all the various fT4 ranges that we have to deal with, it makes it hard to really trust the comparisons.

I know we can make allowances by converting it to % through the range, but your examples here make a bit of a mockery of that idea too.

Personally i still have difficulty accepting that my fT4 level is properly represented using the very narrow [7.9-14] range that my lab now uses.

eg. i'll now get ...............22.7pmol/L [7.9-14] ie. 242% Dose 112.5mcg

in the past i've had....... 22.8pmol/L [9.5-20] ie.126% Dose 150mcg

Both giving me a TSH of 0.04, .....simply does not compute

(and there is a big part of me that still thinks surely a pmol/L is a pmol/l whatever th range is)

Hence my personal opinion that i don't really think individual thyroid blood tests are worth the paper their written on, and we can only tell anything by looking at a series off results . looking for trends in direction, and putting that together with very detailed observation of our personal symptoms, rather than placing too much emphasis on making dose decisions based on any individual result.

[Meanbeannyc in reply to tattybogle]

They like me to be under 1 here... I’m a Graves TT patient.

[tattybogle in reply to Meanbeannyc]

Ah OK ... opposite issue then! they'd want you to increase if they just looked at the 1.23 result.

Hopefully you have a doctor who's looking at the bigger picture not just TSH, cos this is an excellent example of why TSH test alone is not enough.

[Meanbeannyc in reply to tattybogle]

Yes. They would like to see me around 0.5

[shaws Administrator]

The result for T3 can depend on how long you leave between the dose and the test. It also depends upon if it was a fasting or non-fasting test.

The difference in your results is because the labs differ in their ranges.

i.e.

FT4 : 1.74 (0.78-2.19)

FT3: 2.56 (2.77-5.27)

++++++

FT4: 1.6 (0.8-1.8)

FT3: 2.6 (2.3-4.2)

[Meanbeannyc in reply to shaws]

But one is below range and the other in range. I was not on any T3 meds

[thyr01d]

Serendipitious and I have just had this, different results from different labs, with ferritin, which doesn't vary according to medication or anything. Odd and a little worrying.