TSH 3rd generation test result-Help

[palomadp2]

Hello, I just had a blood work and I'm curious about the result of this specific test:

TSH 3rd Generation

Result: (0.016 uUI/mL) Normal range is 0.270 to 4.200 uUI/mL

Background: woman, 50 y.o and with HYPOthyroidism and taking levothyroxine 150 mcg

(T3 levels are normal)

I have schedule to see doctor on monday, but meanwhile I would like to understand why it is so low? As I've been reading a bit about it but it mostly mentions hyperthyroidism issues.

Thanks in advance

[humanbean]

A test gets invented for the first time then someone comes along and improves it, then a few years later someone else improves the test again. Things don't stand still - a test in 2022 will not be (or is unlikely to be) the same test as was used in the 1980s, for example.

I think each stage of the improvements might be called a generation. Sometimes the generation number is given on sheets of test results and sometimes it isn't.

I'm not 100% certain of the above facts, but someone who will be is diogenes .

He was involved in inventing thyroid function tests in years gone by and he and his research team still publish thyroid research. He is Dr John Midgley B.Sc (Leeds) D Phil (Oxford) and is one of the medical advisers for Thyroid UK (the charity which runs this forum).

You can find out more about Dr Midgley on this page :

thyroiduk.org/about-thyroid...

...

Do you have the results and reference ranges for Free T4 and Free T3? If you do could you post them please. Gleaning anything about TSH on its own is virtually impossible.

[palomadp2 in reply to humanbean]

Oh thanks for the reply!The generation thing was roughly translated from the test which is not in english so prob sounded off 😅

As for the t4 and t3 my doctor did not mark them in the order, a mistake I believe.. but I do have:

- Total t3: 125 ng/dL (normal: 80 to 200 ng/dL)

- TPO antibodies: lower than 5 UI/mL (normal: lower than 34 UI/mL)

- Antithyroglobulin antibody: 183.5 UI/mL (normal: max 115 UI/mL)

[diogenes Remembering in reply to humanbean]

The problem with devising a test is that one has to use the knowledge of human biochemistry that was known at the time. The first test for FT4 uncovered situations that the previous tests didn't show up. The chief problem was a condition called FDH, where the albumin in blood has a different form to the usual form. This rare condition has albumin that binds onto T4 about 50 times stronger. This converts the influence of albumin on the test from negligible to one equal to the stronger T4- binding proteins. In the first tests this problem was uncovered. There also were patients on T4 that had powerful antibodies that bound T4 and distorted the test result badly. There were also problems with some nonthyroidal i illness patients. The second generation of tests addressed these issues. By that I mean that the tests I was responsible for were redesigned. Copiers of the FT4 tests weren't so careful, leading to today's problems of consistency.

[tattybogle]

my (very simplistic) understanding of 'first' generation , 'second' generation and 'third' generation TSH test is this :

the 'first' one invented was accurate enough for 'in range' results, but was not very good at accurately measuring very low levels of TSH .

The 'second generation' TSH test was better at measuring lower levels, and the lowest possible result would be eg. TSH 0.01 and anything lower would be reported as <0.01

The 'third generation' TSH test was better than the 'second' at accurately measuring even lower concentrations , so the lowest possible result on a third generation TSH test may be eg TSH 0.001 or 0.005 and anything lower will be reported as <0.001 or <0.005

(in effect ... 'third generation' tests seem to be able to measure down to 3 decimal places , but 2nd generation tests can only measure down to 2 decimal places. ... i think )

As to "why your TSH is below range "... .. if you still feel well on your current dose i wouldn't worry about it too much.

lots of people on levo do end up with their TSH a little bit under range ... but their fT4 and fT3 are comfortably within range.

In patients on Levo, a low TSH doesn't mean quite the same thing as it dose in people who are Hyperthyroid, because taking levo alters the relationship a little .

So in people on levo, you need to look at not just their TSH level, but also whether their fT4 or fT3 levels are really too high for them or not ,and whether they actually have any symptoms of overmedication , or whether they feel well on that dose.

It's not a good idea to adjust Levo dose based only on a TSH result ... you really need a bigger picture.

Once you have found out your fT4 and fT3 levels , you may perhaps want to consider a very small reduction in levo to try to get your TSH to come up a little.. there is evidence from a long term study of people on levo that TSH of 0.04 or higher, has no increased association for heart or bone problems , but TSH of 0.03 or lower does have some increased statistical risks . if you can have a slightly lower dose and still feel well , then that's fine , but if a slightly lower dose makes you feel undermedicated and hypothyroid symptoms return , then it's not worth making yourself unwell just to get your TSH to come up .

For more information see my reply to this post : healthunlocked.com/thyroidu... feeling fine but TSH is low (3rd reply down) it contains a link to that study .. and a list of other psts discussing the subject of low TSH /risk versus quality of life .

[palomadp2 in reply to tattybogle]

Thanks! This is very helpful info, will read the post