How Reference Ranges Work
What Is a Reference Range?
A reference range is derived from testing 95% of healthy people. This means 5% of healthy people fall outside it — so an 'abnormal' result doesn't always mean something is wrong. Context is everything.
The Full Blood Count (FBC) Explained
| Parameter | Normal Range (Adult) | What It Measures |
|---|---|---|
| Haemoglobin (Hb) | Men: 130–170 g/L; Women: 115–155 g/L | Oxygen-carrying protein in red cells |
| White cell count (WBC) | 4.0–11.0 × 10⁹/L | Immune system cells |
| Platelet count | 150–400 × 10⁹/L | Blood clotting cells |
| MCV | 80–100 fL | Red cell size — guides anaemia type |
| Neutrophils | 1.8–7.5 × 10⁹/L | Main bacterial infection fighters |
| Lymphocytes | 1.0–4.0 × 10⁹/L | Virus-fighting cells |
Kidney & Liver Function Tests
| Test | Normal Range | Significance |
|---|---|---|
| Creatinine | 60–110 μmol/L | Kidney filtration waste product |
| eGFR | >60 mL/min/1.73m² | Estimated kidney filtration rate |
| ALT | 7–56 U/L | Liver cell damage marker |
| Bilirubin | <21 μmol/L | Bile pigment — elevated in jaundice |
| Albumin | 35–50 g/L | Nutritional status & liver synthesis |
Trending ResultsA single result means less than a trend. If your creatinine is 130 today but was 70 six months ago, that rising trend is more concerning than the absolute value.
What does 'borderline abnormal' mean?
It means your result is just outside the reference range but not dramatically so. Your doctor will decide whether to retest, monitor, or investigate based on clinical context.
Can I ask for a copy of my blood results?
Yes. In the UK, patients have the right to access their health records. Most GP practices now offer online access via NHS App or Patient Access.
Why do different labs have different reference ranges?
Labs calibrate their own equipment and sometimes use different test methods. Always compare results from the same laboratory.
Should I fast before blood tests?
Only certain tests require fasting (glucose, cholesterol, triglycerides). Your GP or lab will tell you specifically. For a routine FBC or kidney/liver panel, fasting is usually not needed.
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.