Introduction
It’s a scenario many of us recognise, you get a notification that your blood test results are available and open them without a healthcare professional there to help you interpret them. Your eyes are immediately drawn to the one or two red numbers that fall outside the “reference ranges” and you’re wondering what this all means.
What is a reference range?
Initially when lab tests were developed patients’ results were compared to those of supposedly “normal individuals” and the “normal ranges” of those individuals. There was considerable variation between laboratories and patient populations and so the term “reference ranges” was adopted as it better reflects what these intervals provide: a point of reference to help interpret a result, rather than a strict definition of what is “normal”. This is important when looking at your own results, a value outside the reference ranges could mean that this is “normal” for you.
Reference intervals are commonly designed to include the central 95% of results from an appropriately selected reference population, leaving 2.5% above and 2.5% below the interval.
Discover the 5 habits that boost your longevity
Unlock a doctor-reviewed 5-day guide to the core pillars of long-term health—diet, exercise, lifestyle, sleep, and mental wellbeing. Evidence-based, practical, and designed to help you start making meaningful changes today.
No spam. Unsubscribe anytime.
By continuing, you agree to receive occasional updates from Emerald. See our Privacy Policy.
Why one slightly abnormal result might not mean very much?
Having a result above or below the reference range can also often be due to natural biological variation. When you're dehydrated, your plasma volume falls. This can make your haemoglobin concentration and red-cell count appear higher, even though your body hasn't suddenly produced more red blood cells.
Your levels of cortisol vary throughout the day and are highest around waking and decline through the day. Therefore, the time the sample was taken can greatly affect the result.
These examples demonstrate that your individual results can vary because of normal biological variation. A result slightly below or above the reference range may therefore have little clinical significance when considered in isolation.
Context matters more than the red result
After seeing an abnormal result, there are a few things to consider. A result sitting just outside a reference interval is not necessarily clinically significant. How far it lies outside the range, which biomarker is being measured and the wider clinical context all matter.
Does it fit with related results? Individual biomarkers often make more sense when interpreted alongside related tests. For example, an abnormal haemoglobin can be interpreted alongside MCV, ferritin and other relevant results rather than in isolation.
How does it compare with your previous results? If a result has been consistently just outside the reference interval for years, that may mean something different from a result that has suddenly changed from your established baseline.
Does it fit the person? This may be something to discuss with a medical professional who can give you more context to the situation. Certain factors such as age, sex and medications can cause your blood results to fall outside the reference ranges. For example, statins can cause mild elevations in liver enzymes whereas age and sex can influence creatinine due to differences in muscle mass.
Why a “normal result” isn’t always the full story
Often what is more relevant is to look at the trend. Is this result consistent with your previous tests or is this the result of a falling or rising trend. Creatinine levels which are used to assess kidney function, may be showing a month-by-month gradual increase, although the result is still within the normal ranges. An abnormal result isn’t necessarily evidence of disease but a normal result doesn’t necessarily mean there is nothing worth investigating.
Longevity starts with awareness
Less than £1/day. Test 115+ biomarkers. Personalised plan and 1:1 GP support.
The bigger picture
Blood tests are most useful as a picture and not as a collection of isolated numbers. One slightly abnormal result shouldn’t automatically cause alarm, just as a page of results within the reference ranges doesn’t always tell the whole story. What matters is the pattern, trajectory and clinical context. So next time you see a red number on your results, don't just ask whether it's outside the range. Ask how abnormal it is, whether it fits with your other results, how it has changed over time and what it means in the context of you.
Instead of asking… | Ask… |
Is this number red? | How far outside the range is it? |
Is every result normal? | Do the results form a meaningful pattern? |
Was this normal today? | How has it changed over time? |
What does Google say this means? | Does this fit my symptoms and circumstances? |
Related articles
Test 124 biomarkers for fine-tuning your health
See your results in 3 days with high-level accuracy and a certified GP-reviewed action plan