One Lab, same time, 2 requests, same tests. TWO DIFFEREND RESULTS! Why is that?

I had a private BT done at the same day and the same location were my doctors test request was done. ...... TWO different results for the lot!!!!

private :TSH= 0.05 (0.40-4.00) Ft3= 5.9 (2.8-6.8) FT4 = 6 (10-20)

GPs : TSH= 0.01 FT3= 4.6 FT4= 9.6

He ordered THS,T3,T4 and written as test result, was: FT3,FT4 why is that? Printing mistake?

And because he ordered T3 and T4, I have ordered private FT3 and FT4 he said there is no noticeable difference in the ft or t tests, that is why he ordered the way he did.

did I wasted au$80?

Don't forget: both results done same time, same office, same lab!!! should i complain to someone , but whom???

At the practice, after i told him my self medicating with S-Thyroid.... he straight away told me to stop what i was doing (friendly tone) and take 1 NDT and half a t3. Blood test in 6 weeks, after the test, 2 NDT only and another test in 8 weeks after the first.

I am not converting t4 well enough that's why i got the t3. he said, because of the NDT my body (Thyroid) is converting better. I was kind of in shock, to take 2 NDTs as i never got up to more then 125 of t4.

Should I think positive about this new regime [in 6 weeks time?] ? 2-NDTs are ca 160-t4 and ca 20-t3 am I right?

BtW, my vit result are upper range thanks to vit supplements.

Thanks for making the effort of reading and answering in the sweltering heat that europe is going through.

It is winter in Queensland......20 at daytime....11 at night and it is FREEZING!!

39 Replies

cannot explain the different lab results but have no quibble with what your doctor is suggesting

Are the lab ranges the same? If so get in touch with the lab and point this out.

Most labs these days do Free T4 and Free T3 rather than Total T4 and Total T3. So "T4" is simply assumed as Free T4, and similarly for T3. If the lab were one that does Total T3, then they would have assumed TT3!

Labs vary. That is why each and every lab has its own reference ranges.

Were the samples drawn at the same time?

Biotin (vitamin B7) affects lab results. Some tests do not get affected, others do. Did you take a significant amount in the days leading up to the tests?

helvella, it was taken :

same office

same blood

same time

same lab

no vitamin 7 yet, will start with the multies next week.

no biotin neither.......weired.

That's worrying and shows that there is some inaccuracy in the lab results . Do you know who the lab are. Can you ask them how accurate their tests are supposed to be and if this level of variation is within their expected range? . surely there must be some kind of quality control at the lab where the tests are done,


i just wrote to the office were I ordered my privat test from (cost me horryfying au$338, hormones and b12 as well) I did not complain, as it isn't his fault, but have ask him, if he has ever heard of a mixed up result like mine ? waiting his replay.

how can we trust the results......ever?

my doctor didn't know of the privat result, but i will go back to him next week, as he didn't print out the lot of test results. i take my private result to show him as well!. x

Very disappointing.. I hope you get some answers.

I had two different results from the same NHS lab with same blood taken at same time and even tested at same time. One was for gp the other for endo. One was high one was low. I told gp endo and lab. They did not understand or care. Endo looked at his results and said increase gp looked at his and said no way and I eas stuck in the middle.


that tells us some thing, doesn't it!

You did not state the range in the other one. If done on different machine which is calibrated differently it could be different but with mine even if done on two machines they should both show low in range or both high in range not one high and one low.

lilian, they were done in the same lab with the same ranges.

what happened after your opposite results? are you feeling better now?

Are you absolutely certain they were done in the same lab and that the private ones weren't sent somewhere else? As mentioned, check the reference ranges for the second test as might be different.

yes saggy, same office, same time, same blood, same lab. one was for the BT the gp gave me and one was my private one.

Are you in the UK? My private ones that I pay for from medichecks or blue horizon are always done at a different lab even though I get blood done at the same place so a little confused?

If they were done by same lab, all you can do is ask them?

i am in Australia and the organisation was 'iMedical'[[they have their own nurses stations]] the lap was QML, what is a very big lab with lots of nurses stations and labs all over the place. i just looked at my result sheet and there is a phone number. I am going to ring and point this mishap out to them. maybe i am lucky and get an explanation. thank you Saggy x

Washed my hands of them and buying own NDT. When I complained to the lab she offered me a new test. She did not get the sarcasm when I asked which machine she would be testing me on.

lillian, you are a champ!!

i am not very observant in everything, and just now i answered a question about my ranges and looked it up on my exel page...checked on the printout..and guess what! ... two slightly differend ranges!! that is the problem. i imagined, that it was done on a different machine, but assumed, same make and model!!!

you solved the problem here and you got through my slow fogged up brain!


If I have read you right, two grains of desiccated thyroid are closer to 80 micrograms of T4 than the 160 you wrote.

But yes, T3 will be about 20 micrograms from two grains of desiccated thyroid.


😳, math was never my strong point!!

i am soo glad the t4 will not be that high.

thank you. x

Please keep us informed

silverfox, lilliana solved it. i had to check my exel page for the t3 and rT3 ratio...then doubble checked on the lab printouts...and voila(tatata) two differend "in range" numbers. it said it clear and loud: two differend machines. same lab, differend machine.

the gp's was finished 10am and mine was done at 3.49pm

I think those finishing times are very significant.

a) If "yours" hung around for at least 4 hours in an un-airconditioned environment I think you could expect different results.

b) T3 "decays" faster than T4 in the body (half life of 8 hours +/-) I am not sure if the same thing happens if it sits around in a test tube (air conditioned or not) if it does, then this would account for the lower reading of T3 in "yours".

For the FT4, we would have to check to see if they measured in the same units, e.g. ng/dL or pmol/? If the units are different then that is the reason the numbers are different. Have another look and let us know.

I have had blood tests by my GP and Functional doctor taken at the same time by the same pathology lab in Brisbane, Douglass (depending what State there are other partners - the company logo is the red strand of DNA). No problems at all when the blood was taken at the same time as the results sent to both doctors were the same but ordered on different referrals.

Explained to the pathology practice why I was doing that and she entered a note on the computer system that the doctors were only to receive their requested results.

I had a personal relationship with this collection office because I had been ill for so long with blood drawn every 2 weeks at one point because my GP was trying to find what was wrong.

I always have it taken fasting and as close to 7.30am as possible.

The reason I had the two bloods taken was so I could see what each doctor thought.

GP said results very normal, functional doc said there were multiple problems. I have only become well with medical treatment from my functional doctor.

My latest tests (3rd set since being in Port Macquarie New South Wales) were done by the same sister lab and are consistent with the same ranges. I have been told the calibration of their machines are the same over all their labs.

So not sure what is happening for you.

maybe i will write to the lab and as for an explanation. need my head/brain for that to work and of course some confidence and energy...... i got both done in 'imedical'

I do not know imedical. My functional doc insists that blood is drawn fasting and at the same time for every test. He wanted close to 8am but the collection clinic made a mistake on my first blood draw because the nurse did not read all his instructions. I arrived early because the traffic flow was good that morning. Now I have them done as close to 7.30 as possible.

He explained it was for comparison reasons so he has a better understanding what the body is doing. That is also why I use the same company in each State. So far it is working for me and I also check the ranges which is consistant with all the collection clinics run by this company.

Last bloods all was good except I now have loe cholestrol but have stopped the Lipitor. Naturopath said everything else except glucose readings and B12 were OK. B12 was in range but she said the active B12 would be low at that reading. Now taking under the tounge spray. Lab does not do active B12 unless reading is not in range , even though the doctor asked for it to be done.

When I go back to Brisbane I will have my Queensland lab card renewed (issued by the lab as easy reference for the collection centre) my original card was in my handbag that was stolen. I have one for New South Wales so will be interesting to see if the patient number is the same. Anyway it will make it easier as we travel as I need bloods done every six months for other conditions. Now done to 3 because my blood sugar has risen.

Even when I have test done for my GP I keep to the fasting (if he asks but it is usual) and time then everything is consistent.

Over here Finland where I live tests are run in different labs even though they are done in same lab.

So, even if me and my dad go to same lab, same tests , same time, mine are ran in that lab as the request comes from my GP. But my dad unless going to GP has the request from central hospital where he is treated otherwise, so his tests are sent to another lab.

If we go and have thyroid test at the same time I get my results in an hour and my dad gets them 8 hours later.

But if I have more tests ran they are sent to another lab as my local lab can only run basic tests. Maybe yours were sent to another location as it was a part of larger set of tests. Otherwise I can't understand they would charge you from same tests. It doesn't make sense.


That would explain different results as then the method can change. In some cases these modern quick tests tend to overestimate the ft4 and ft3 especially on the lower end. Antibodies to T3 or T4 could affect as well.

Immunoassays (the normal tests done) are not acutaly that precise! So this is sadly unsurprising. Simply having done one test immediately and the other a few hours later without preserving the blood could cause some varation.

The inaccuracies are worse for smaller values (like your TSH) but your T4 was a bit surprising.

The lesson here for us all is to rember that lab results are a guide, but symptoms are king!

thank you all for your input. i will get to the bottom of it.

edit: same lab, different make and model machines, as the range's () are slidly different!. love you all to try hard to get to the bottom of the two different results.

thank you all again 💕💐👍😍

Just one small point: I would not bother about differences in the TSH results. The reason is that anything under .5 will be challenging the resolution of the equipment. TSH between 1 and up is like using a ruler to measure a piece of string, it can be quite accurate. Trying to measure TSH below 0.5 is like trying to measure the thickness of a butterfly's wing with same ruler - for that job you would need a micrometer. Now, fiddling around between .001 and .05 is meaningless which is probably why the equivalent of a micrometer for TSH hasn't been built (at least outside of a research lab).

Looking on the bright side however, at least you have a doc who knows that NDT and T3 only, exists!

thank you LAH, that is a really good titbit of knowlege! my doc didn't mind my 0.05 for a long time, but the result he was send was 0.01..... and he fliped. the result i was send was 0.05....

Wonder if that's the reason we are not allowed a very low TSH because the machines are inaccurate at that point!!!! (Said very tongue in cheek!).

We already see TSH results with ridiculous number of decimal places - I certainly do not believe that the analysis is truly verified and repeatable to two decimal places, let alone three.

The extract below suggests 0.01 as the functional sensitivity of TSH tests. Many TSH tests are reported with a comment such as "3rd generation". Bit the extract also points out that lot to lot variability of the reagents used is a significant issue.

Functional Sensitivity (FS) – determines the lowest reportable assay limit

During the period of active TSH assay improvement, different non-isotopic IMAs made competing claims for sensitivity. Methods were described as: “sensitive”, “highly sensitive”, “ultrasensitive” or “supersensitive” – marketing terms that had no scientific definition. This confusion led to a debate concerning what was the most clinically relevant parameter to use to determine the lowest reliable reportable TSH value for clinical practice [8,397-403]. Functional sensitivity (FS), defined as the lowest analyte concentration measured with 20 percent coefficient of variation [24] is now recognized as the parameter that best represents the between-run precision for measuring low analyte concentrations in clinical practice [24,395,404]. FS is used to define the lower clinical reporting limit for not only for TSH assays, but also Tg and TgAb measurements, for which assay sensitivity is critical [8,24,397,404,405]. Protocols used for establishing FS specify that precision be determined in human serum, not quality control materials based on artificial protein matrices, since immunoassays tend to be matrix-sensitive [406,407]. The time-span used for determining precision is also analyte-specific and should reflect the frequency of testing employed in clinical practice – 6 to 8 weeks for TSH, but 6 to 12 months for the Tg and TgAb assays when used as tumor markers for monitoring differentiated thyroid cancer (DTC). This time-span is important because low-end, between-run assay precision erodes over time as a result of a myriad of variables, reagent lot-to-lot variability being a key variable [9,408-410]. Note that the FS parameter is more stringent than other biochemical sensitivity parameters such as limit of detection (LOD – a within-run parameter) and limit of quantitation (LOQ – a between-run parameter without stipulations regarding matrix and time-span for determining precision) [404,411]. A ten-fold difference in FS has been used to define each more sensitive “generation” of TSH [397] or Tg [32,404,412,413] method. Thus, TSH RIA methods with FS approximating 1.0 mIU/L were designated “first generation”, TSH IMA methods with functional sensitivity approximating 0.1 mIU/L were designated “second generation”, and TSH IMAs with FS approximating 0.01 mIU/L are designated “third generation” assays [8,57,395,397,405,414]. Analogous to TSH, Tg assays [Section 6A] with FS approximating 1 μg/L are designated “first generation”, whereas Tg IMAs with FS approximating 0.10 μg/L meet the criteria for a “second generation” method [32,58,296,395,404,413,415,416].

i think they are getting so scientific, so we mere morals don't know what is going on. don't think the health professionals see through it neither.

Even manufacturers don't claim better than 0.1 for TSH...


Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to synthesize and secrete thyroid hormone. TSH serum measurements are used to detect primary hypo- and hyperthyroidism. The capability of a TSH assay to distinguish between normal and subnormal concentrations is essential for thyroid testing strategy. Quantification of TSH at a lower value of 0.01 mlU/L yields information that is useful to clinicians referring patients with subnormal TSH concentrations. Siemens’ TSH assays consistently deliver sensitive, highly specific results, across multiple platforms.

Basicallyt Mojas, all machines that meaure stuff in blood produce a slghtly diferent 'signal' inside them for the same blood sample. Its true for Thyroid tests, its also true for blood meters.

Rather than use a sample with a known about of TSH to calibrate the machine and produce an accurate result what they do is test a large number of 'healthy' volunteers and work out the 'normal range' that way.

Because each machine (due to differences in brand, or age of machine) will respond differently to the same blood samples, each has its own unique normal range (my cousin's wife used to work in a lab :- ).

Great paper Helv, look forward to reading that when brain is loss 'foggy' due to heat... :-)


who knows 😉😏🙃🤔

Saw a comment recently that mentioned third generation and not come across it before so thanks for the explanation!

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