I often post the text and link below on HealthUnlocked because it is one of the best papers about reference intervals - normal ranges.
Because
it comes from the medical world, written by medics and published in the
British Medical Journal, it should be convincing to healthcare
professionals.
It is also written in a way that is reasonably accessible to many patients, at least with a bit of careful reading.
The normal range: it is not normal and it is not a range
Abstract
The
NHS ’Choose Wisely’ campaign places greater emphasis on the
clinician-patient dialogue. Patients are often in receipt of their
laboratory data and want to know whether they are normal. But what is
meant by normal? Comparator data, to a measured value, are colloquially
known as the ’normal range’. It is often assumed that a result outside
this limit signals disease and a result within health. However, this
range is correctly termed the ’reference interval’. The clinical risk
from a measured value is continuous, not binary. The reference interval
provides a point of reference against which to interpret an individual’s
results—rather than defining normality itself. This article discusses
the theory of normality—and describes that it is relative and
situational. The concept of normality being not an absolute state
influenced the development of the reference interval. We conclude with
suggestions to optimise the use and interpretation of the reference
interval, thereby facilitating greater patient understanding
►Health is a relative and not an absolute state.
►The
reference interval acts as a comparator for the patient’s blood result.
It is not the arbiter of whether disease is present or not.
►Natural fluctuations in a blood result can occur.
►Comparison of a result against the reference interval should be informed by the clinical suspicion made beforehand.
The full paper is freely accessible here and it is highly recommended that you read it:
https://academic.oup.com/pmj/article/94/1117/613/6959235?searchresult=1
There is also a reasonable video which might help:
There is also a very good talk on thyroid testing by David Halsall
Additional links regarding reference intervals:
Biochemical bigotry: Enforcing normalized thyroid lab results
Thyrotoxicosis can occur with high or normal TSH?
https://thyroidpatients.ca/2019/07/04/thyrotoxicosis-can-occur-with-high-or-normal-tsh/
To link from HealthUnlocked, copy the entire red text below and paste into a post or reply.
This is a link to a very good article in the British Medical Journal discussing what the 'normal range' really is. Very readable.
[i][b]The normal range: it is not normal and it is not a range[/b]
This blog has the abstract of this paper plus link to the original full paper. Also includes some extra links to a video and some other related information.
Last updated 10/02/2025[/i]
Link to blog:
https://helvella.blogspot.com/p/the-normal-range-it-is-not-normal-and.html
If you find anything incorrect, misleading, typos, links that don’t work, etc., please let me know. Go to my profile and use the contact details there.
