Blood tests deciphered

What your blood count actually measures

When your GP orders a “blood count”, they usually mean the small blood count (CBC). It counts your red and white blood cells and measures haemoglobin and haematocrit. In short: it checks whether your blood is basically working. It checks whether enough oxygen is being transported and whether your immune system is responding. No more, no less.

The large blood count (CBC with differential) adds a differential, i.e. the split of your white blood cells into subgroups such as neutrophils, lymphocytes and monocytes. That is useful for infections, allergies or certain blood disorders. But here too: not a word about ferritin, not a word about vitamin D, not a word about the thyroid.

The problem? Those are exactly the values that tell you why you are tired, why your hair is falling out, why you are not losing weight. Or why you simply do not feel the way you think you should.

What is not measured

Let me be specific. The standard blood count contains neither ferritin, nor vitamin D, nor TSH, nor HbA1c. Those are all values you have to request extra. Or that your doctor only orders when there is a concrete suspicion. In everyday statutory care there is simply no budget for them.

Ferritin is your iron store. The lab reference range often starts at 15 ng/ml. At aescolab we see the optimal range for women at 50–130 ng/ml and for men at 100–250 ng/ml. The difference is huge: you can have a ferritin of 20, the doctor says “normal”, and you can barely get out of bed in the morning. A randomised study of 198 women shows: at ferritin below 50 ng/ml, iron substitution reduced fatigue by almost 48%, versus 29% on placebo (Vaucher et al. 2012 [1]).

Vitamin D? Almost never measured routinely, even though it is involved in hundreds of metabolic processes. The standard range starts at 30 ng/ml. The optimal range at aescolab is 50–80 ng/ml. And this is where it gets interesting: a European study of more than 55,000 people from 18 population studies shows that 40% of Europeans have a vitamin D level below 50 nmol/L, i.e. in the deficiency range (Cashman et al. 2016 [4]). Forty percent. And most people do not know, because nobody measures it. More on that in our vitamin D guide.

TSH, the thyroid marker? Standard range 0.35–4.94 mU/l. Optimal: 0.5–2.5 mU/l. You can have been fighting a subclinical underactive thyroid for years at a TSH of 4.0, with symptoms such as weight gain, cold sensitivity and brain fog. And your blood count says: all good.

HbA1c, your long-term blood sugar? Standard “normal” up to 5.7%. The optimal range is 4.8–5.3%. That means your metabolism can already be out of balance long before the doctor flags it as a problem.

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Targeted, not a watering can

The standard blood count is not bad. It is just not built for your question. It was developed to rule out acute disease: anaemia, infections, leukaemia. Not to tell you why you feel at 80% instead of 100%.

An extended blood panel, of the kind we offer at aescolab, takes a completely different path. Instead of 5–10 values we measure more than 50 biomarkers: from ferritin to vitamin D, omega-3 index, HbA1c, thyroid values, liver markers and inflammatory parameters such as hsCRP. And we do not only compare with the lab reference range, but with optimal ranges based on scientific evidence.

The reference range tells you: you are not ill. The optimal range tells you: here you can still do something. That is the difference between “everything is fine” and “this is how you get more out of your body.” Why that is a problem, we explain in Your values are all normal.

Measure, act, measure. That is my mantra. We look at your values, derive concrete steps, and after three months we check whether anything has changed. No guessing, no watering-can approach. And that is exactly the difference from a one-off blood test at the GP that then disappears in a drawer.

What the research says

A meta-analysis by Yokoi & Konomi (2017) [2] confirms: iron deficiency without anaemia — exactly the range the standard blood count does not cover — is a relevant cause of fatigue. The pooled effect size from six randomised trials was significant (0.33; 95% CI 0.17–0.48). That means: even if your haemoglobin is normal, a low iron store can still be responsible for your exhaustion.

Garcia-Casal et al. (2018) [3] show in a WHO-supported systematic review: current ferritin cut-offs systematically underestimate true iron status. Healthy people with empty bone-marrow iron had a mean ferritin of only 15.1 µg/L, right on the standard lower limit. The study recommends raising the cut-offs.

The Cashman study (2016) [4] with more than 55,000 European participants shows: 13% have a vitamin D level below 30 nmol/L (severe deficiency) and 40% below 50 nmol/L (insufficiency). In the European winter, prevalence of severe deficiency rises to almost 18%. That is not a niche. That is a mass phenomenon that stays invisible in the standard blood count.

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Frequently asked questions

Is the small blood count enough to spot deficiencies?

No. The small blood count measures cell counts and haemoglobin, but not nutrients, hormones or inflammatory markers. For a statement on ferritin, vitamin D or the thyroid you need additional parameters.

Why does my doctor not automatically order ferritin and vitamin D?

Because those values are not part of the routine check. They have to be requested specifically. In many cases a medical justification is needed, and the insurer only covers the cost when there is a well-founded suspicion. At aescolab they are standard in every panel.

What does “optimal range” mean compared with the “reference range”?

The reference range covers the middle 95% of the population, including people with subclinical deficiencies. The optimal range is oriented towards values that research associates with the best physical and mental performance.

How often should I have my blood tested?

I recommend a check every 3–6 months, especially if you are actively working on your health. That way you see whether measures are working, and you can adjust instead of operating in the dark.