Why your blood tests might not be giving you the full picture

I wonder if this sounds familiar?

You’ve have a few health concerns recently, and decided to go to see your GP. They encouragingly sent you for a whole range of blood tests, but when the results came back, they told you that everything was ‘normal’ and ‘within range’. You were sent on your merry way with a clean bill of health and no further action required. 

But you still aren’t feeling great, and you’ve got a niggling suspicion that something isn’t right with your health. 

No, you’re not going crazy. Even if nothing was flagged up by the GP with your bloods, it’s feasible that those blood tests are only giving you one piece of the picture. 

In this article I’ll explain why being within the ‘normal’ range isn’t necessarily the end of the story when it comes to blood tests. 

Conventional laboratory reference ranges vs optimal ranges

So what is ‘normal’ anyway, and how does this differ from ‘optimal’ when it comes to our health? 

Reference ranges are a useful tool when interpreting blood test results, designed to help healthcare practitioners identify and diagnose disease and deficiencies. The ‘normal’ reference range is a range that is considered normal for a healthy person – and this ‘normal’ range is based on the range that 95% of the population fall into. 

This bell curve shows the distribution for the ‘normal’ range, where you can see the 95% of the population being ‘normal’ (the pink area). The 5% outside that would be outside the normal range: 

How is the ‘normal’ range determined?

Firstly, the population used to identify the ‘normal’ range might not be as healthy as we’d like. Remember when I said that 95% of the population falls within the normal reference range? This means that, over time, as the population gets sicker with more health issues, the number of people who fall within this ‘clinically normal’ range becomes larger. Then the ‘normal’ range becomes relative to a sick population. 

Is everything really ‘normal’?

There is a big difference between not having a disease, and being in a state of optimal health. Often, when you get your blood tests back from the GP, they won’t flag the fact that you are near the bottom or top end of the reference range. Technically, you are ‘within range’, but this might not be a ‘normal’ result for you, or might indicate the early signs of imbalance or disease. Often it takes years to get to this diseased state, for example in the case of thyroid disorders or diabetes, but in the meantime, you might have been told that everything is normal. 

What are your health goals?

It also depends what your health goals are. Let’s take fertility as an example. The optimal reference ranges for someone trying to conceive and grow a healthy baby might be very different to the ‘normal’ reference range for the rest of the population to avoid deficiency. 

For example, when we look at vitamin D3, the NICE guidance says that blood levels of less than 25 nmol/L indicate an increased risk of vitamin D deficiency, while 25-50 may be inadequate in some people. Vitamin D levels are ‘sufficient’ for most people when levels are greater than 50 nmol/L. But this range is looking at the risk of osteoporosis and other bone diseases. In fact, research suggests that the optimal range when trying to conceive is significantly higher – at least 100nmol/L.[1] 

We also want our total vitamin B12 to be over 350 ng/L when trying to conceive. In a study of IVF patients, women had the highest chance of live birth when their serum B12 was over 700 ng/L.[2] The NHS range says over 200 ng/L is unlikely to suggest B12 deficiency, and for many women, that’s the end of the road. However, finding this out sooner could potentially be an easy win when trying to conceive, by increasing B12 levels safely through diet. 

Why be normal when you could be optimal?! Being ‘normal’ might mean you don’t have a disease or deficiency, but this might also be a long way from optimal health – where we feel balanced, energised, and well enough to live a long, healthy, disease-free life. For example, your ferritin (iron stores) and vitamin B12 might be the low end of the ‘normal’ range, contributing to tiredness and fatigue. Yes, you might not be classed as anaemic, but for many, this low-level tiredness can be very real and debilitating.  

Optimal ranges can also give clues about the root cause and what might be driving some of your symptoms. Rather than a black and white approach (either in or out of range), we want to look at the whole picture, to try to get to the root cause of any health issues. For example, if you eat a healthy, balanced diet but your levels of vitamins and minerals are on the low end of the normal range, this might indicate that you’re not absorbing these nutrients properly. This might suggest that we need to look at supporting gut health. 

We are all unique, and what is considered ‘normal’ will vary from person to person, depending on factors like age, gender, ethnic background, and lifestyle. People within the ‘normal’ range are assumed to have no clinical signs and symptoms of any disease. However, this isn’t always the case. 

Prevention is better than cure. Often, conventional reference ranges don’t take into account your risk of developing a disease or your life expectancy. With Nutritional Therapy, we aim to do everything we can with diet and lifestyle to keep the body as healthy as possible, for as long as possible, helping to reduce the risk of diseases and illnesses as far as we can. 

To summarise, here is a comparison of conventional reference ranges vs optimal ranges:

Conventional laboratory reference ranges	Optimal ranges
Used to identify and diagnose disease states and pathology	Linked to better health and longevity
Usually based on the range that 95% of the population fall into	Based on scientific evidence and clinical guidelines
Indicates disease / pathology	Indicates dysregulation / imbalances before patient ends up in the diseased state

Blood tests are still incredibly useful, and this article is not designed to discourage anyone from going to see their GP with their health concerns. 

We should all have access to our blood test results, so if you’re just told over the phone by the GP receptionist that everything is normal, ask to see the actual results. You should also be given the reference ranges, so you can see where you fit into this. 

When interpreting these tests, it can be helpful to dig a little deeper beyond the ‘normal’ result. You might want to seek support for this, as piecing together all this information can be really complex and confusing! As a Nutritional Therapist, I like to take everything in the context of the optimal range, along with any symptoms, family history, health history, food diary and lifestyle to see whether there might be some imbalances or dysregulation going on that can be supported with diet and lifestyle. 

If you have any questions, please do get in touch, or book in for your free 30-minute hormone review here.

Please note, this blog should not be taken as medical advice. If you have any health concerns, please consult a medical professional. 

References

[1] Wagner CL, Baggerly C, McDonnell SL, Baggerly L, Hamilton SA, Winkler J, Warner G, Rodriguez C, Shary JR, Smith PG, Hollis BW. Post-hoc comparison of vitamin D status at three timepoints during pregnancy demonstrates lower risk of preterm birth with higher vitamin D closer to delivery. The Journal of steroid biochemistry and molecular biology. 2015 Apr 1;148:256-60.

[2] Cirillo M, Fucci R, Rubini S, Coccia ME, Fatini C. 5-methyltetrahydrofolate and vitamin B12 supplementation is associated with clinical pregnancy and live birth in women undergoing assisted reproductive technology. International journal of environmental research and public health. 2021 Nov 23;18(23):12280.