Thyroid UK
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Why do labs use different ranges?

This whole subject is so complex. So why the extra burden of different labs using different ranges to evaluate the efficiency/effectiveness of our constituent blood parts? I'm sure this question must have been put before. Why can't they all use the same ranges and compare like with like to try to simplify it. Am I stupid for thinking this?

5 Replies

Hi Kicker, this is because they use different equipment, there are a number of different equipment manufacturers out there, and the same as the reagents, it is the manufacturer that establishes the reference range used for each test analysed on their equipment not the lab.


You are not stupid in thinking this at all! I am annoyed that the range varies from lab to lab. Should be one standard range across the country.

Ann xx


It's not just a case of the equipment used at the lab, it also depends on the way that the reference range was calculated. Deciding what's 'normal' and what isn't is far more difficult than it might first appear. In general, the reference range for most tests is the range that 95% of apparently healthy people fall into. The upper limit of TSH quoted by some labs may be too high due the inclusion of people with subclinical hypothyroidism in the sample of volunteers used to calculate the range.


It certainly is not just you wanting the results to be consistent across labs, and across countries:

At least within the UK labs tend to use the same units for measurements - even if they have different reference ranges. Anyone trying to understand medical papers from the rest of the world first needs to consider whether the tests are the same, the units, the reference ranges and the clinical implications all need to be thought about.



Hi They often use different assays, so long as you always have the ranges it is fine. However, of course, simpler to try and keep to one Lab. if possible,



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