The normal range: it is not normal and it is not a range - BMJ article Nov 2018 by Martin Brunel Whyte & Philip Kelly

[MaisieGray]

More from bloody-mindedness and frustration, than an expectation that it would make a blind bit of difference to his understanding or future decision-making, like a parrot, I once spent a whole appointment saying "reference interval" every time the locum GP said "normal range" ....... The title is largely self-explanatory; this is a useful and easy to read paper about the dreaded "normal range". For those less familiar with the issues raised, it might help underpin more constructive dialogue with the GP when trying to explain why we aren't necessarily optimally medicated, never mind healthy, just because our result falls anywhere between two numbers.

Conclusion

The reference interval is an extremely useful means of contextualising a patient’s result but it is wrong to automatically assume ‘normality’ of a result within that interval, just as it is wrong to assume abnormality outside of the interval. Normality is relative and situational. With understanding of the nature of the reference interval, logical decisions can be made that will improve the effectiveness of the clinical consultation.

Main messages

- 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.

pmj.bmj.com/content/postgra...

Apologies if it has been posted previously.

[Mamapea1]

Thank you for posting👍.

[helvella Administrator Thyroid UK]

Another issue with the phrase "normal range" is that appears to invite those who see it written to treat it as a statistical normal distribution (also call Gaussian distribution). Often referred to as the bell curve. The TSH distribution is NOT a Gaussian distribution. It is inappropriate to use the standard deviations, etc. of a Gaussian distribution on TSH statisitics.

[MaisieGray in reply to helvella]

Agree. The author put it this way Third, the bell-shaped distribution that we term the ‘normal

distribution’ is something of a misnomer. It was commonly

referred to as ‘Gaussian’ until another mathematician, Karl Pearson, adopted the term ‘normal distribution’, referring to the fact that the distribution pattern was ubiquitous in life. The term was not introduced for its propensity to identify ‘normal’ individuals. For instance, a blood urea value at the upper end of the reference interval may represent significant renal impairment in an individual who has liver dysfunction and cannot adequately synthesise urea.

[Hillwoman]

Thanks for posting. I couldn't help smiling when you referred to your determination to use the term 'reference interval' with your GP. I've done exactly the same, but a puzzled stare was the only response. I don't think they know what the difference means. 😏