Blood test results explained: a plain English guide for UK patients.

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.

The four columns of every result

Column	What it means
Marker name	The specific substance being measured, for example haemoglobin, TSH or 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 means above range, L means below range. A star or exclamation mark means 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): glucose, cholesterol, electrolytes
• µmol/L (micromoles per litre): creatinine, bilirubin, uric acid
• g/L (grams per litre): haemoglobin, total protein
• IU/L (international units per litre): liver enzymes such as ALT, AST and ALP
• mIU/L (milli international units per litre): TSH, the main thyroid marker
• nmol/L (nanomoles per litre): vitamin D, testosterone, cortisol
• pmol/L (picomoles per litre): the thyroid hormones T3 and T4
• pg/mL (picograms per millilitre): B12 and 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.

UK panels at a glance

Panel	What it includes
FBC	Full Blood Count: red cells, white cells, platelets, haemoglobin, haematocrit.
U&E	Urea and Electrolytes: sodium, potassium, urea, creatinine and eGFR for kidney function.
LFTs	Liver Function Tests: ALT, AST, ALP, GGT, bilirubin, albumin, total protein.
TFTs	Thyroid Function Tests: TSH, sometimes T4 and T3.
Lipids	Total cholesterol, LDL, HDL, triglycerides and non HDL cholesterol.
HbA1c	Average blood sugar over the last two to three months.
Iron studies	Serum iron, ferritin, TIBC and 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 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 through 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.