I try to keep going to the same clinic so blood tests retain comparability.
Annoyingly the clinic has changed its reference range.
T4 starts at 9.0 now instead of 12.0.
T3 tops out at 5.7 whereas before it was 6.8.
Now I’m confused when comparing results in different points in time.
I’ll post my results in a later post but trying to understand, for example, if someone had a T3 of 6.5, that would be within the old reference range but now would come up as outside the range based on the new range.
So potentially someone could end up with a reduced dose due to change in reference range?
With so few patients on T3 treatment anyway, I wonder if the reference ranges take into account the T3 levels of such patients given ref ranges generally strip out the top and bottom 2.5% of the population.
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Wired123
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If someone had a result of 6.5, just under top of range, then we should expect one of two possibilities:
A result just under the top of the new reference interval. Maybe about 5.5. If the reference interval is performing similarly just the numbers have changed, this is likely.
Or a result similar to 6.5 but now falling outwith the reference interval. This would suggest that the analysis is more rigorous and some results which were formerly high-ish are now being excluded.
Interesting so in scenario 1 the person would have a different result even if they did the result a day apart (ie, the day before ref range changed and the day of the change in ref range). So in effect 2 things are changing at the same time.
How does this work? I thought the ref ranges were simply based on the population passing through that lab’s doors and the top and bottom 2.5% of results (outliers) are excluded to fix the range. Pretty unscientific and arbitrary.
I didn’t think that the actual level the machine reports would change as the blood level is still the blood level.
TSH tests were affected by antibodies to TSH itself as well as some other antibodies.
Hence, a TSH result from someone with those particular antibodies would see a higher result than if they did not have those antibodies. It would be a falsely elevated result caused by interference by antibodies.
However, two factors come into play. Some tests are more affected than others. Which makes the results somewhat random (from one manufacturers' system to another). And also on average somewhat high.
As manufacturers took action to make the testing process less susceptible to this interference, several things would happen.
Reference intervals would tighten and have lower top ends.
An individual having their blood tested before and after the test improvement might see a lower result. If they have relevant antibodies, the result should drop. But if it was a genuine result, it should remain the same but would look higher compared with the new top of reference interval. So the mean will drop but not every individual's tests will drop.
This is just one hyper-simplified example.
The process of improving and changing tests hasn't just been a single change. Tests are updated from time to time. An individual manufacturer might have updated their test two, three or more times over the years. Each update might have had an impact of reference intervals, on susceptibility to antibody interference, or both.
In the end, we really have to go with new reference intervals. And the best we can hope is to look at where in the reference interval or result lies. That is, the percentage through.
You can play around with this:
helvella - Range Calculator Spreadsheet
A spreadsheet for calculating a test result as a percentage through the reference interval (range).
This is an Excel spreadsheet but is likely to work in other spreadsheet software.
The lab isn’t changing. It’s the same lab. They have changed their ref range hence the question.
In the past I’ve seen myself get very similar results despite going to different labs, but each lab would have its own ref range based on the population that passes through it.
Would be interesting to see how the same equipment can get different ranges dependent on the genetic make up of the local population in each location.
What does the ref range look like in a majority “white” area vs say London with its more multicultural mix of ethnicities?
The lab isn’t changing. It’s the same lab. They have changed their ref range hence the question.
Yes, I know and it should have read
So if you are 70% through one lab range you will be 70% through another lab range regardless of what that range is
But a sneaky 's crept in as I'm using my tablet with predictive text rather than my PC.
My GP surgery changed it's range a few years ago from 11.8 - 24.6 to 7-17 and results were similar percentage through range. Similarly with using private labs with range of 12 - 22 the percentage through range is roughly the same as my surgery.
Ok that’s useful to know but annoying as I track my results on a spreadsheet, not just thyroid but about 25 different things and it looks like most ref ranges have changed
You can probably do sum functions to convert them all to percentages so they are like for like. It’s not too difficult you just do the sum function and apply it to all the relevant cells so should be easier than doing it all one by one. It’s ages since I did all that stuff so can’t be more specific. There must be a true spreadsheet nerd on here that could help you!
Yes, mine are all on a spreadsheet too. I have one page for thyroid, one for vitamins and one for "other" (I have to have regular other tests for something else), so I toggle between them when I'm adding the different tests.
I just add an extra column for the percentage.
If I've had the thyroid tests done with the private lab I just look at the result as I know the ranges are the same, if I have one done at my GP surgery with the different range I just look at the percentage.
Lordly, I hope not, they already did that and increased it to 10 some time ago, can't remember what it was before, I hope they don't increase it ever again.
We have many tests done at different clinics and hospitals; sometimes the ranges are the same as those done at our local lab, sometimes not. Occasionally ranges themselves have changed, but it is the actual position of your result within each range that is important.
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