Blood Test Results Explained: How to Read Your Report
Short answer: each line of a blood test report shows a marker, your result, the unit it is measured in and a reference range. Results outside the range are usually flagged H (high) or L (low). A flag is a prompt to look closer, not a diagnosis: what matters is how far outside the range the result is, whether it fits your symptoms and how it compares with your previous results.
The parts of a blood test report
Marker: what was measured, for example haemoglobin, ferritin or TSH.
Result and unit: your value, such as 14 µg/L or 5.2 mmol/L. Always compare like with like, because the same marker can be reported in different units.
Reference range: the range found in most healthy people, set by the laboratory that ran your test. Use the range printed on your own report.
Flag: H or L when a result is above or below that range.
Reference ranges cover about 95% of healthy people, so roughly 1 in 20 healthy people will be outside the range for any single marker. That is why one mildly flagged result is common. Read more in out of range does not always mean abnormal.
Common markers and what they mean
Full blood count (FBC)
Counts red cells, white cells and platelets, and checks for anaemia and signs of infection. See our guide: full blood count explained.
Ferritin (iron stores)
Shows how much iron your body has stored. UK guidance uses a ferritin below 30 µg/L to confirm iron deficiency, but ferritin rises with inflammation, so a 'normal' result does not always rule it out. Read: low ferritin: what it means and what to do next.
Vitamin D
In the UK, a level below 25 nmol/L is generally treated as deficient, and 25 to 50 nmol/L may be inadequate for some people. Levels are often lower in winter.
HbA1c (average blood sugar)
Reflects your average blood sugar over about three months. Below 42 mmol/mol is normal, 42 to 47 mmol/mol suggests a higher risk of type 2 diabetes (often called prediabetes), and 48 mmol/mol or above is in the diabetes range and needs confirming and follow-up.
Cholesterol
Total cholesterol of 5 mmol/L or below is generally considered healthy for adults, but the breakdown (HDL, LDL, non-HDL and triglycerides) and your overall heart risk matter more than a single number.
Thyroid (TSH and FT4)
TSH is the main screening test. A high TSH can suggest an underactive thyroid and a low TSH an overactive one. Ranges vary between laboratories, and borderline results are often repeated before any decision is made.
Kidney (eGFR) and liver (ALT)
An eGFR of 60 or more is usually fine; an eGFR below 60 that stays low for three months or more can indicate chronic kidney disease. A raised ALT can follow alcohol, some medicines, fatty liver or recent hard exercise, and is usually rechecked.
CRP (inflammation)
Rises with infection or inflammation anywhere in the body. Read: the CRP blood test explained.
When to get your results explained
A result is flagged and you are not sure whether it matters
Everything is 'normal' but you still feel unwell
Several markers have changed since your last test
You want to know what to do next, or whether you need treatment or a retest
Our Advanced Clinical Practitioner can go through your whole report with you, by phone anywhere in the UK from £50 or face to face in Crewe, and a prescription is included if it is right for you. Book a results consultation.
Frequently asked questions
Why are my reference ranges different from someone else's?
Laboratories use different equipment and reference populations, and some ranges depend on age and sex. Always read your result against the range on your own report.
Should I worry about one result that is slightly high or low?
Usually not on its own. Small changes are common and are often rechecked. The pattern across your report, your symptoms and your previous results matter more.
Can I get results from another provider explained?
Yes. Bring or send the report to your consultation and the clinician will go through it with you.
This article is general information based on UK guidance from the NHS and NICE. It is not personal medical advice. If you are worried about a result or have symptoms, speak to a clinician. In an emergency call 999.
