Understanding your results
How to Read Your Blood Test Results: A UK Guide
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed April 202615 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
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Blood test reports list each biomarker against a reference range, the middle 95% of a healthy population. In range means statistically normal, not necessarily optimal for you. Check the pattern across related markers. Retest before acting on one abnormal result. And share anything well out of range with your GP.
Your results land in your inbox or NHS App, and suddenly you are staring at a wall of abbreviations, numbers, and reference ranges that mean nothing to you. Your GP says “everything looks fine.” But what does “fine” actually mean?
This guide explains how to read a blood test report. It covers the common UK biomarkers, what reference ranges mean (and why they are not the same as optimal), and when a result needs attention. It draws on NHS, NICE, and BMJ clinical guidance.
What is a blood test actually measuring?
A blood test measures specific substances in your blood: proteins, hormones, vitamins, minerals, enzymes, fats, sugars, and cell counts. Each substance is a biomarker, and each shows how one system is working.
Take ferritin, which measures iron stores. A low ferritin does not mean you are anaemic yet, but it can explain fatigue and brain fog weeks before your haemoglobin drops far enough for a GP to flag it.
A standard NHS test checks around 10 markers. A broader panel spans hormones, thyroid, inflammation, liver, kidney, vitamins, and metabolic health. More markers means a more complete picture.
What do reference ranges mean?
Every result comes with a reference range: two numbers that define “normal.” The NHS range for TSH is typically 0.27–4.2 mIU/L.
These ranges come from testing a large group of healthy people and taking the middle 95%. So 2.5% of healthy people fall above the range and 2.5% below, even when nothing is wrong. The BMJ calls them “not diagnostic thresholds” but statistical distributions.
“The reference range is defined as the interval in which some proportion (frequently 95%) of measurements from a healthy population is expected to fall.”
— American Journal of Epidemiology (2022)
Ranges also vary between labs, because they use different analysers. The NICE thyroid guidelines say to read results against your own lab's range, not a generic one from Google.
Key point:“in range” means you are within the statistical norm. It does not mean your level is ideal for you.
Why “normal” doesn't mean optimal
This is the most important idea in reading blood results. The standard range shows whether you likely have a disease, not whether you are at your best.
Take vitamin D. The NHS calls anything above 25 nmol/L “sufficient.” But the Endocrine Society recommends 75–150 nmol/L for immunity, bone density, and mood. You can be in range at 30 and still feel terrible.
The same goes for ferritin. The NHS lower limit is around 15 µg/L, but active people feel better above 50–80. A level of 20 will not flag, yet it can explain chronic fatigue.
Performance ranges narrow the window from “not sick” to “thriving.” Helvy reports plot your results against both the clinical and performance range, so you see the gap.
Full blood count (FBC)
The full blood count is the most ordered blood test in the UK. It measures red cells, white cells, haemoglobin, and platelets, and the NHS uses it to screen for anaemia, infection, and blood disorders.
| Marker | Typical range | What it tells you |
|---|---|---|
| Haemoglobin (Hb) | Men: 130–170 g/L Women: 120–150 g/L | Oxygen-carrying capacity. Low = possible anaemia. |
| White blood cells (WBC) | 4.0–11.0 ×10⁹/L | Immune activity. High may signal infection or inflammation. |
| Platelets | 150–400 ×10⁹/L | Clotting ability. Very low = bleeding risk; very high = clotting risk. |
| MCV | 80–100 fL | Size of red blood cells. Low = possible iron deficiency. High = possible B12/folate deficiency. |
What to watch for:low haemoglobin with low MCV usually means iron-deficiency anaemia, the UK's most common nutritional deficiency (WHO). High MCV with low haemoglobin often points to vitamin B12 or folate deficiency.
Liver function tests (LFTs)
Liver function tests measure enzymes and proteins the liver makes. The key ones are ALT, AST, GGT, ALP, bilirubin, and albumin.
ALT is the most liver-specific enzyme. The NICE guidelines on fatty liver disease recommend testing ALT in routine health checks. A normal ALT is below 40 IU/L for men and 32 for women.
Common causes of raised enzymes: alcohol, fatty liver disease, medications, intense exercise, and viral infections.
What to watch for: a lasting ALT above twice the upper limit needs investigation. A single mild rise after a hard week is usually fine; recheck it.
Kidney function tests
Kidney tests usually include creatinine and eGFR, urea, and electrolytes. eGFR is the key marker: it estimates how well your kidneys filter waste.
An eGFR above 90 is normal. Between 60 and 89 may mean early decline, especially if it lasts three months. Below 60 is chronic kidney disease, per NICE.
What to watch for:creatinine rises with muscle mass, so muscular people can have a falsely low eGFR. If you lift and your eGFR is 75–85, that may be normal for you.
Thyroid function (TSH, T3, T4)
Your thyroid controls your metabolic rate, energy, and temperature. The TSH test is the standard screen, and NICE recommends it first-line for suspected thyroid problems.
The TSH range is typically 0.27–4.2 mIU/L, but growing evidence puts the optimal range at 0.5–2.5. A TSH of 3.8 is technically “normal” but can mean your thyroid is starting to struggle, especially with symptoms.
Why TSH alone isn't enough:TSH shows how hard your pituitary is working, not how much active thyroid hormone (free T3 and free T4) is circulating. A full thyroid panel should include TSH, free T4, and ideally free T3. Helvy's General Energy & Wellness panel covers TSH and free T4; our Thyroid & Vital Organs panel adds free T3.
What to watch for:TSH above 4.0 with symptoms needs investigation. Subclinical hypothyroidism (TSH 4–10 with normal T4) affects about 5–8% of UK adults, per the British Thyroid Foundation.
Cholesterol and lipid profile
A lipid panel measures total, LDL, and HDL cholesterol plus triglycerides. The NHS targets total cholesterol below 5 mmol/L and LDL below 3.
But total cholesterol is a blunt instrument. ApoB is a better heart-risk marker, because it counts the harmful particles themselves, not just cholesterol mass. The European Society of Cardiology now recommends ApoB alongside standard lipids.
Lp(a) is a genetic heart risk factor most NHS tests skip. A raised Lp(a) sharply increases risk regardless of LDL, and you test it once.
What to watch for: the triglyceride-to-HDL ratio predicts metabolic health better than any single lipid number. Below 1.0 (mmol/L) is excellent; above 2.0 needs attention.
Vitamins and minerals
The most tested nutritional biomarkers in the UK are vitamin D, vitamin B12, folate, ferritin, magnesium, and zinc.
| Nutrient | NHS “normal” | Optimal range | Why it matters |
|---|---|---|---|
| Vitamin D | > 25 nmol/L | 75–150 nmol/L | Immunity, mood, bone density, muscle function |
| Vitamin B12 | > 180 ng/L | 400–700 ng/L | Energy, nerve function, red blood cell production |
| Ferritin | > 15 µg/L | 50–150 µg/L | Iron stores, energy, oxygen transport, recovery |
| Folate | > 3.9 µg/L | > 10 µg/L | Cell division, DNA synthesis, pregnancy health |
| Magnesium | 0.7–1.0 mmol/L | 0.85–1.0 mmol/L | Sleep quality, recovery, muscle relaxation, calm |
| Zinc | 11–24 µmol/L | 14–20 µmol/L | Immune function, testosterone production, wound healing |
Notice the gap between NHS “normal” and optimal. Most people live there: in range, but not at their best. A wider test with performance ranges makes that gap visible.
Hormones (testosterone, cortisol, DHEA-S)
Testosterone is the marker most men ask about. The NHS range, roughly 8.6–29 nmol/L, is enormously wide. A 35-year-old at 10 is “normal” but likely has fatigue and poor recovery.
Cortisol is your main stress hormone. It should peak in the morning, typically 166–507 nmol/L. Consistently high suggests chronic stress; low may point to adrenal fatigue (a pattern, not a diagnosis).
DHEA-S is a precursor to testosterone and oestrogen that declines from your late twenties. A low DHEA-S for your age can point to faster ageing.
What to watch for: read hormones together. Low testosterone with high SHBG tells a different story from low testosterone with low SHBG. Symptoms matter as much as the number.
Inflammation markers (CRP, hs-CRP)
High-sensitivity CRP (hs-CRP) measures low-grade inflammation, the kind with no symptoms that tracks heart risk, metabolic problems, and ageing.
The British Heart Foundation treats hs-CRP as a useful add-on. Below 1.0 mg/L is low risk; 1.0–3.0 moderate; above 3.0 high.
What to watch for: a single high hs-CRP does not mean heart disease. It can spike after infection, hard exercise, or poor sleep, so the trend matters. If it stays above 1.0, look at your lifestyle.
Blood sugar and HbA1c
HbA1c measures your average blood sugar over 2–3 months. It is the gold standard for diabetes screening and the best single metabolic marker.
The NICE diabetes guidelines set the thresholds: below 42 mmol/mol is normal, 42–47 pre-diabetic, 48 or above diabetic. But research in the Lancet Diabetes & Endocrinology shows heart risk rising above 37 mmol/mol, well within “normal.”
What to watch for: an HbA1c of 40 will not flag, but it is a yellow light. With raised triglycerides and a large waist, it suggests early metabolic trouble that lifestyle can reverse.
What to do when results are flagged
A flagged result, one outside the reference range, is not an automatic cause for alarm. A structured approach:
- 1.
Don't panic at one result
One abnormal reading could be a lab error, a fluctuation, or something you did the day before, like heavy exercise or alcohol. Retest before drawing conclusions.
- 2.
Look at the pattern
A vitamin D of 30 nmol/L in January is expected; the same level in August is more concerning. Trends beat any single snapshot.
- 3.
Consider context
Age, sex, activity, medications, and recent illness all affect results. A creatinine that looks abnormal for a sedentary 60-year-old may be normal for a 30-year-old who lifts.
- 4.
Talk to someone qualified
If a result is well outside range, speak to your GP or the reviewing doctor. Every Helvy test is analysed at UKAS-accredited UK labs that flag anything needing follow-up.
- 5.
Retest in 8–12 weeks
If you change supplements, diet, or training, retest after 2–3 months to confirm it worked. Most people test once and never follow up.
Frequently asked questions
Can I trust the results from a home blood test?
Yes. Reputable home blood test providers (including Helvy) process samples at UKAS-accredited laboratories — the same accreditation standard as NHS pathology services. The finger-prick method has been validated against venous blood draws for the vast majority of biomarkers.
Do I need to fast before a blood test?
For most biomarkers, fasting isn’t required. However, if your test includes a lipid profile (cholesterol and triglycerides) or fasting glucose, a 10–12 hour overnight fast will give the most accurate results. HbA1c does not require fasting. Helvy’s instructions will specify whether fasting is recommended for your panel.
What time of day should I take a blood test?
Ideally in the morning, before 10am. Testosterone, cortisol, and iron all follow a circadian rhythm — they’re highest in the early morning and decline throughout the day. Testing at the same time each time ensures your results are comparable.
My results are all “in range” but I still feel terrible. What now?
This is extremely common. Standard reference ranges are designed to detect disease, not to identify suboptimal levels. A wider panel read against the optimal ranges longevity researchers use — not just the disease thresholds — can reveal where you sit relative to “thriving”, not just “not sick.” Vitamin D, ferritin, B12, and thyroid are the most common culprits.
How often should I get a blood test?
For most healthy adults, once or twice a year is a sensible baseline. If you’re actively optimising (changing diet, supplementing, training hard), testing every 3 months lets you measure what’s working. Read our full guide on testing frequency.
Should I share my results with my GP?
Absolutely. Private blood test results complement NHS care — they don’t replace it. If anything comes back significantly out of range, your GP should know. Most GPs welcome private results as additional data points, though they may want to confirm with their own lab if treatment is being considered.
Ready to see the full picture?
Helvy reads your markers against the optimal ranges longevity researchers use. UKAS-accredited UK labs analyse every result, and you get recommendations tailored to what your blood shows. Results usually within 5 working days of sample receipt.
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Medical disclaimer
This guide is for general educational purposes and does not constitute medical advice. Blood test results should always be interpreted by a qualified healthcare professional in the context of your individual health history. If you have concerns about any blood test result, consult your GP or the doctor reviewing your results. Helvy blood tests are analysed at UKAS-accredited UK laboratories to ISO 15189.