Standard NHS panels are designed to identify serious pathology. They use population-derived reference ranges that include unwell people. Between "nothing serious found" and "actually well" lies a functional territory that functional blood chemistry interpretation reveals — insulin resistance, subclinical hypothyroidism, early inflammation, and nutrient insufficiency invisible to standard analysis.
The NHS standard blood panel is one of the most efficient diagnostic tools in primary care. A full blood count, basic metabolic panel, liver function tests, thyroid screen, and lipid panel can collectively identify anaemia, kidney disease, liver pathology, diabetes, hypothyroidism, and dyslipidaemia from a single blood draw. For detecting serious illness at the pathological level, it is genuinely excellent.
But the reference ranges it uses are population-derived — calculated from the distribution of results in the tested population, including people who are unwell, medicated, or metabolically compromised. A result within the "normal" range means you are within the range seen in that population. It does not mean you are at the level where physiology functions optimally. These are fundamentally different statements, and confusing them is the source of enormous clinical under-detection.
Ranges matter, but not every tighter band is better. Consider TSH. A typical NHS range is 0.5–4.5 mIU/L, and some practitioners call 1.0–2.0 “functional optimal”. I don’t: no outcome study supports that band, TSH rises with age, and in people aged 85 a higher TSH went with longer survival (Gussekloo 2004). Subclinical hypothyroidism means a TSH above the lab range with a normal free T4. A TSH of 4.2 with fatigue is a reason to look at free T4, free T3 and the rest of the picture, not a diagnosis. Ferritin is the opposite case: there, the evidence supports looking above the lab’s lower limit. In the table, each working band says where it comes from.
| Marker | Lab Normal | Working band (source) | What it means |
|---|---|---|---|
| TSH | 0.5–4.5 mIU/L | Lab range; no tighter band | Subclinical hypothyroidism means TSH above the range with normal free T4. Higher TSH within range went with longer survival in people aged 85 (Gussekloo 2004) |
| Ferritin | 12–300 ng/mL | Below 15 = stores absent; below 30 = low stores, deficiency likely (BSG 2021; Mast 1998); 50–100 my clinical target | In non-anaemic women with fatigue, iron helped only when ferritin was 50 or below (Verdon 2003). The upper bound is my choice, not a proven optimum |
| Vitamin D | >50 nmol/L sufficient | 75–125 nmol/L (30–50 ng/mL), my working range | No guideline sets an optimal level, and trials haven’t shown benefit from aiming higher (Demay 2024). The 125–175 nmol/L once given here had no source. |
| Fasting glucose | 3.9–5.5 mmol/L | Below 5.6 mmol/L (100 mg/dL) usual; 5.6–6.9 (100–125) impaired (ADA 2025) | Read with fasting insulin and HbA1c; a single result can wobble |
| hsCRP | <10 mg/L (standard CRP) | Below 1 mg/L lower risk; 1–3 average; above 3 higher (CDC/AHA 2003) | Above 10 usually means a current infection or injury: repeat when well |
| Homocysteine | 5–15 µmol/L | My flag: above about 11 µmol/L | In older adults with memory problems, B vitamins slowed brain shrinkage most when homocysteine was above 13 (Smith 2010). Lowering it hasn’t been shown to prevent heart attacks |
| B12 | 200–900 pg/mL | 600–1000 pg/mL (= ng/L), my clinical target | A low-normal result may need a second test (active B12 or MMA) to decide |
Insulin resistance is closely linked to type 2 diabetes, metabolic syndrome, PCOS, non-alcoholic fatty liver disease, cardiovascular disease, and increasingly Alzheimer’s disease. In the Whitehall II study, insulin sensitivity fell steeply over the 5 years before type 2 diabetes was diagnosed, while fasting glucose rose sharply only in the last 3 (Tabák 2009). During those years, fasting glucose and HbA1c may be completely normal while insulin resistance is already causing measurable damage.
The standard NHS panel does not include fasting insulin. Without fasting insulin, HOMA-IR (the insulin resistance index) cannot be calculated. Without HOMA-IR, insulin resistance is invisible in the blood work — until it isn’t, and HbA1c has crossed 48 mmol/mol and the diagnosis is type 2 diabetes.
The TG:HDL ratio (triglycerides divided by HDL cholesterol) is a surrogate marker for insulin resistance and small dense LDL particle predominance — both available from standard lipid panels. There is no agreed cut-off in UK mmol/L units, so I read it as a trend alongside fasting insulin. This is information already in the standard blood test that is rarely interpreted this way.
The NHS blood panel is an excellent screen for serious pathology. It was never designed to detect the early-stage functional dysregulation that precedes that pathology by years. That is not its failure — it is simply not the question it was built to answer.
Regenerus comprehensive blood chemistry provides the functional picture: fasting insulin, HOMA-IR, hs-CRP, homocysteine, free T3 and T4, vitamin D at accurate 25-OH level, ferritin with functional interpretation, NLR, and the lipid panel. ApoB and Lp(a) come from the cardiometabolic add-on. These are not exotic tests — they are standard markers interpreted through a functional lens and measured with appropriate sensitivity. The 57-marker Regenerus panel provides a solid foundation; functional interpretation by a practitioner who reads each marker against the lab range and a labelled working band is what turns that data into clinical action.
The DH TDG Five-Test Programme investigates the territory that standard investigation doesn’t reach. Ask AIdan which tests apply to your situation.
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