Medical blood test reference ranges: What “normal” blood tests really mean and why it is failing you.

Oct 9, 2025

4 min read

Shelley-gawith-explaining-blood-tests-to-detox-clients

You’ve probably heard it before or experienced it first hand.

“Your blood test results are normal. You’re fine.”

But if you’re still feeling tired, foggy, puffy, anxious, inflamed, or just off, then what are you meant to do? It’s the most unempowering statement a practitioner can give you. You have gone to them with symptoms and based on numbers, they have basically told you, you can’t trust your body and what it’s telling you, and it’s all in your mind.

Here’s the truth:

Medical reference ranges are based on population averages (so depending on how many sick people are in your population sample, this will be dragging down your mean). These ranges are not based on optimal health, let alone setting you up to THRIVE in life. Let’s pick serum iron, for example, as this reference range is easy. The range is 10-30. Well you might be at 10 and told you are fine. That’s a big difference in both how you feel and just the numbers between 10 and 29, both in the medical reference ranges.

Let’s break down where the ranges for blood tests come from, how often they’re updated (spoiler: not often), and why they might be missing what your body is telling you.

First, what is a reference range for blood tests?

A reference range is the set of values that medical labs consider “normal” for a particular blood marker, like TSH, iron, B12, liver enzymes, or cholesterol.

But here's the catch:

These ranges are created by collecting results from a large sample of people and using statistical methods to define what’s “average.”

Usually, the “normal range” captures the middle 95% of results in that population.

Sounds fine, right? Until you realise…

Shelley-chatting-with-detox-day-clients-about-blood-tests

...Who are these ranges based on?

Reference populations often include:

Hospital patients
Chronically unwell individuals
People with undiagnosed or early-stage conditions
People on medications

In other words: not exactly the type of PERSON you want to become when you optimise your health. Reference ranges are measuring DISEASE not optimising your health.

This means you could be:

Low in iron, but still in the “normal” bucket
Struggling with thyroid symptoms, but your TSH is technically within range
Chronically stressed, but your cortisol or magnesium haven’t hit disease-level lows (yet)

How often are reference ranges for blood tests updated?

This varies by country, marker, and lab. But overall?

Updates are rare and usually very slow.

In Australia and New Zealand, ranges are influenced by guidelines from:

The Royal College of Pathologists of Australasia (RCPA)
The National Pathology Accreditation Advisory Council (NPAAC)
Local hospital data and individual lab statistics
Broader guidelines, such as those in the NHMRC Nutrient Reference Values

But most updates come only when there’s overwhelming new evidence or when lab technology changes drastically. That can take years or decades.

Example: The TSH reference range used to go up to 5.5. Many functional practitioners now consider 0.5–2.5 mIU/L to be optimal but the conventional range hasn’t shifted significantly.

The big problem: Disease vs. function

Medical ranges for blood tests are designed to:

Detect disease
Flag immediate clinical risk
Guide pharmaceutical decisions

They are not designed to:

Track early dysfunction
Optimise energy, mood, hormones, digestion, or longevity
Help you feel your absolute best

So when your GP says, “Everything looks fine,” they’re not wrong.

They’re just reading your results through a disease lens, not a wellness lens.

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Here's a few examples of some common medical ranges.

Have a look at how big the ranges for blood tests can be.

Marker	Medical Range (Example)
TSH (thyroid)	0.5 – 5.0 mIU/L
Ferritin (iron)	30 – 300 µg/L
B12 (serum)	140 – 700 pmol/L
Vitamin D	50 – 250 nmol/L
Magnesium (serum)	0.7 – 1.1 mmol/L

Shelley’s perspective

In clinic, I’ve seen hundreds of clients be dismissed by “normal” labs.

But when we dig deeper, we see:

Low active B12
Poor iron absorption
Thyroid under-functioning long before it hits disease
Magnesium and zinc depletion that drives stress, anxiety, poor sleep, and PMS

Just because something isn’t a diagnosis yet doesn’t mean you should ignore it. In fact, it’s the perfect time. Before it becomes a DISEASE, you can FIX it and transform your health. RIGHT now! It’s the perfect time to get EMPOWERED.

What to ask for

If you’re getting tested, here’s how to make it count:

Always ask for copies of your lab results and make sure you keep them on file so you are in control of your own health. Any lab you go to, have your blood taken you can always ask for a copy of your results to be emailed out to yourself.

I have all my clients track patterns. That’s the amazing thing about blood work, they aren’t just numbers, but when you fall in love with these numbers like I get all my clients to, you can track patterns and be PREVENTATIVE in your health approach. You get to be super empowered, and you don’t need to live in FEAR OF disease. Instead, when you track your own blood tests, you can spot patterns and act early.

When clients are at maintenance levels with their health, I encourage clients to do annual blood tests so that they can track any significant changes to their bodies and take proactive steps. If something else is happening in their body, i/e, pregnancy, menopause, chronic sickness, injuries or anything else out of the ordinary, we might run tests at different times.

Also, please note this is for maintenance. When your body is healing in your Bio Precision Report, you might be recommended to do your blood tests earlier so you can see the success of our nutrients. It will help you stay focused and on track for quick results. We always want to have you feeling amazing as fast as possible.

And as always: test, don’t guess.