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Why do blood test results and reference ranges vary?

Is it possible to arrange for private blood tests via AXA Health? I've had a range or symptoms that could either be thyroid or anaemia related and my GP blood tests are 'all clear'. However I understand that the levels for diagnosis via the NHS are considerably different and are handled as all clear even if there are indicators?

2 October 2019

Blood test reference ranges can vary between different laboratories in the United Kingdom. This is because different laboratories use different equipment and testing methods.

It is important to remember that a reference range does not mean a ‘normal range’ and that this is where some confusion exists in patients interpreting blood test results. Reference ranges vary between different populations and this is also a complicating factor.

A reference range can vary between different laboratories when a collection of people who are considered ‘normal’ are used to establish a reference range for a given blood test. Complex mathematics are applied to allow for a natural variation within this chosen collection of people and therefore the reference range.

A test result can lie outside the reference range. A blood test result that lies outside a reference range does not necessary mean that there is a disease process requiring treatment.

Another complicating factor when reviewing blood test results is that there can be ‘false’ positive results and ‘false negative’ results. Blood test results need to be interpreted in relation to other blood test results undertaken and often blood tests need to be repeated.

Blood test results can also be affected by age and gender. It is also possible that test results can vary due to the time of day the blood test is taken and whether you have eaten or not.

All blood test results need to be reviewed by a clinician who is familiar with a given laboratory’s reference ranges and a disease process.


In order to obtain blood tests via AXA Health and your private medical insurance, you would need to be referred by your treating general practitioner to a consultant in the relevant clinical specialism. Please contact your Personal Advisory Team in the usual manner to authorise treatment with your policy.

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