Thyroid UK
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Some "GCSE" questions on lab ranges from a novice

On a steep learning curve……..bear with me!

I am aware that when you get a print-out of your test results the lab ranges are usually in brackets (lowest to highest) next to your actual results. I initially assumed that these ranges were “standard”, but I’m also picking up now that this is not necessarily the case.

I read today that “to create a reference range, a number of volunteers (usually over 120) are matched for factors such as age, gender and ethnicity, and the analyte of interest [had to look this up – the constituent that they are interested in - like Ferritin] is then measured”

What I understand by this is that a middle-aged female patient would be likely to have her blood test results measured against a different set of lab ranges than say a teenage male patient.

What I don’t get is why does the range differ from lab to lab? or does it....? Environmental factors?? Or do different labs use different scales? Or do scales change??? I recently received a print-out which seemed to suggest this (i.e., for the last 13 years my Hb has fluctuated between 9.9 and 14.8 - a series of 29 blood tests - then suddenly in March 2013 it shot up to 122. This latest March result did come with some ranges (115-165) so what was going on for the last 13 years?)

Most importantly, does this also mean that looking on the internet for standard ranges is a bit of a waste of time??

I AM learning that the simple solution is to always get a print-out.

Any help gratefully received.

2 Replies

For some tests there are specific range by age, gender, ethnicity, etc. but, other than in paediatrics, these seem to be the exception.

The whole process of testing would, ideally, use perfectly standardised test samples so that the lab could calibrate everything. They would use the same units in every lab. And son on. But truth is there are too many ways in which tests vary however much effort has been put in to avoid that.

It is fundamentally true that test ranges are established by relatively small groups. But over the years and decades real values from real tests do get repeatedly analysed to see if anything looks wrong. For example, maybe among undiagnosed/untreated patients the lab might see 10% over the top of the TSH range. If the next month they see 0% or 40% then there clearly is a question that need answering.

Some tests do have very standard ranges around the world. The only reference range that really matters is the one from your lab.

We have seen the top of the TSH range drop significantly over the past, say, decade. At least some of that was improvements to tests to exclude people with thyroid issues and, specifically, antibodies to TSH itself causing too high results. (This was achieved by "filtering" out the THS-plus-antibody lump known as macro-TSH before testing the remainder.)



Many thanks for your response Rod. Your sentence - "the only reference range that really matters is the one from your lab" confirms for me the importance of getting that print-out!!


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