Your blood test results arrive as a table of numbers, abbreviations, and flags. For most people, they are difficult to interpret — not because the information is hidden, but because no one has explained the structure. This guide walks through everything you need to know to read your results confidently.
The anatomy of a blood test result
A standard blood test result contains four key columns: the name of the marker being measured, your result, the reference range (sometimes called the normal range), and a flag indicating whether your result is within, above, or below that range.
| Column | What it means |
|---|---|
| Marker name | The specific substance being measured (e.g. Haemoglobin, TSH, Ferritin) |
| Your result | The measured value, expressed in specific units |
| Reference range | The range considered normal for the general population tested at that lab |
| Flag (H / L / *) | H = above range, L = below range, * or ! = significantly outside range |
Understanding reference ranges
Reference ranges are not universal medical thresholds. They are statistical ranges derived from a sample of the general population — typically the middle 95% of results from healthy adults. This means that by definition, 5% of healthy people will fall outside the reference range on any given test, purely by chance.
Reference ranges also vary between laboratories, because different labs use different equipment, reagents, and population samples. A ferritin result of 14 µg/L might be flagged as low at one lab and within range at another. This is one reason why comparing results across different providers requires care.
Common units and what they mean
Blood test results use a variety of units depending on what is being measured. The most common are:
- mmol/L (millimoles per litre) — used for glucose, cholesterol, electrolytes
- µmol/L (micromoles per litre) — used for creatinine, bilirubin, uric acid
- g/L (grams per litre) — used for haemoglobin, total protein
- IU/L (international units per litre) — used for liver enzymes (ALT, AST, ALP)
- mIU/L (milli-international units per litre) — used for TSH (thyroid)
- nmol/L (nanomoles per litre) — used for vitamin D, testosterone, cortisol
- pmol/L (picomoles per litre) — used for T3, T4 (thyroid hormones)
- pg/mL (picograms per millilitre) — used for B12, some hormones
The most common blood test panels
Most NHS and private blood tests are grouped into panels. Understanding which panel you had helps you know what was and was not tested.
| Panel | What it includes |
|---|---|
| Full Blood Count (FBC) | Red cells, white cells, platelets, haemoglobin, haematocrit |
| Urea & Electrolytes (U&E) | Sodium, potassium, urea, creatinine, eGFR (kidney function) |
| Liver Function Tests (LFTs) | ALT, AST, ALP, GGT, bilirubin, albumin, total protein |
| Thyroid Function Tests (TFTs) | TSH, sometimes T4 and T3 |
| Lipid profile | Total cholesterol, LDL, HDL, triglycerides, non-HDL cholesterol |
| HbA1c | Average blood sugar over 2–3 months |
| Iron studies | Serum iron, ferritin, TIBC, transferrin saturation |
Why "normal" sometimes feels wrong
Many people receive results within the reference range but continue to feel unwell. This is not unusual, and it does not mean the results are wrong. It reflects the limitations of population-based reference ranges when applied to an individual.
Several factors can mean a result within range is not optimal for you: your personal baseline may naturally sit at the lower or upper end of the range; your symptoms may be driven by a combination of markers that each look normal individually; or your results may be trending in a concerning direction even though they have not yet crossed a threshold.
What to do with your results
If any result is flagged, your GP will usually contact you. If you have online access to your NHS records (via the NHS App), you can view results directly — but without context, a flag can cause unnecessary anxiety. Before acting on any result, it is worth understanding what the marker measures, what the flag means in the context of your health, and what questions to ask your GP.
biomarkr is designed to help with exactly this: it explains each marker in plain English, shows you how it has changed over time, and identifies patterns across markers that a single result cannot reveal.
Track this marker over time, not just today
biomarkr keeps every result in one place and shows you the direction each marker is heading — free for your first year.