Blood Test Results Explained: The Complete UK Guide

Quick Summary

Most blood test results are straightforward — once you know what the abbreviations mean and where the normal UK ranges sit

Your GP won't always explain every number — so we break down the 9 most common panels in plain English with UK reference ranges

One abnormal result rarely means something serious — context, trends, and how you feel matter more than a single snapshot

Private blood tests start from around £39 — check our comparison of private testing services if you want to track your own health

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You've just opened a blood test results letter (or stared at a confusing online dashboard) and half the numbers might as well be in a foreign language. FBC, ALT, TSH, eGFR — none of it means anything unless someone actually explains it.

Short Answer: Blood test results explained UK-style means understanding about 9 key panels: full blood count, cholesterol, liver function, kidney function, thyroid, HbA1c, iron and ferritin, vitamin D, and CRP. Each has UK-specific reference ranges (mmol/L for cholesterol, IU/L for liver enzymes). Most results fall within normal ranges, and a single slightly off reading usually isn't cause for panic — your GP looks at the overall picture.

What blood test results actually tell you

Blood tests are a snapshot of what's happening inside your body right now. They measure things like how well your organs are working, whether you're low on specific nutrients, and whether there are signs of inflammation or infection.

In the UK, your GP will usually request blood tests if you have symptoms, as part of a routine check, or for monitoring an ongoing condition. The results come back with a reference range — the "normal" window for each marker. If your result sits inside that range, you're typically fine. If it sits outside, it might need a closer look.

Two things worth knowing upfront. Reference ranges can vary slightly between labs. And a single result outside the normal range doesn't automatically mean something is wrong — stress, dehydration, recent meals, and even the time of day you had the test can all shift your numbers.

Full blood count (FBC)

The full blood count is the most common blood test in the UK. It measures the cells in your blood: red cells, white cells, and platelets.

What each marker means

Marker	What It Measures	Normal UK Range
Haemoglobin (Hb)	Oxygen-carrying protein in red cells	Men: 130–170 g/L, Women: 120–150 g/L
White blood cells (WBC)	Immune system activity	4.0–11.0 x10⁹/L
Platelets (PLT)	Blood clotting ability	150–400 x10⁹/L
Red blood cells (RBC)	Total red cell count	Men: 4.5–5.5 x10¹²/L, Women: 3.8–4.8 x10¹²/L
MCV	Average size of red cells	80–100 fL

Low haemoglobin usually means anaemia — you might feel tired, short of breath, or pale. It's common in women, shift workers with poor diets, and anyone not eating enough iron-rich food.

High white blood cells can mean your body is fighting an infection. It can also be raised temporarily by stress or exercise. Persistently high levels need further investigation.

MCV tells your GP what type of anaemia you might have. Low MCV points toward iron deficiency. High MCV can suggest B12 or folate deficiency.

Cholesterol panel (lipid profile)

Cholesterol testing in the UK uses mmol/L (not mg/dL like in the US — worth knowing if you're comparing results online).

Marker	What It Measures	Ideal UK Level
Total cholesterol	All cholesterol combined	Below 5 mmol/L
HDL ("good" cholesterol)	Protective cholesterol	Above 1.0 mmol/L (men), above 1.2 mmol/L (women)
LDL ("bad" cholesterol)	Artery-clogging cholesterol	Below 3 mmol/L
Triglycerides	Fat in the blood from food	Below 2.3 mmol/L (fasting)
Total cholesterol/HDL ratio	Overall risk picture	Below 6 (ideally below 4)

The total cholesterol number on its own is fairly meaningless. What matters is the ratio between good and bad cholesterol. You can have a total cholesterol of 5.5 mmol/L and be absolutely fine if your HDL is high. Equally, 4.8 mmol/L might be concerning if most of it is LDL.

Triglycerides are heavily affected by what you ate before the test, alcohol intake, and how much sugar is in your diet. A fasting test gives the most accurate reading.

Liver function tests (LFTs)

Liver function tests check how well your liver is working and whether there's any damage or inflammation.

Marker	What It Measures	Normal UK Range
ALT (alanine transferase)	Liver cell damage	7–56 IU/L
AST (aspartate transferase)	Liver or muscle damage	10–40 IU/L
ALP (alkaline phosphatase)	Bile duct function	44–147 IU/L
GGT (gamma-GT)	Liver stress, often alcohol-related	Men: 8–61 IU/L, Women: 5–36 IU/L
Albumin	Protein made by the liver	35–50 g/L
Bilirubin	Waste product from red cell breakdown	3–17 µmol/L

GGT is the one that tends to spike with regular alcohol use. If your GP sees raised GGT alongside raised ALT, they'll want to talk about your drinking habits. Be honest — they're not there to judge, they're trying to help.

Slightly raised ALT on its own is extremely common and often harmless. It can go up after exercise, with certain medications (paracetamol, statins), or if you're carrying extra weight around your middle. A single raised reading usually gets rechecked in a few weeks.

High bilirubin with everything else normal? That's often Gilbert's syndrome — a harmless genetic condition that affects about 5% of the UK population. Your eyes might occasionally look slightly yellow, but it doesn't need treatment.

Kidney function tests (U&Es)

U&Es (urea and electrolytes) check how well your kidneys are filtering waste from your blood.

Marker	What It Measures	Normal UK Range
Creatinine	Waste product from muscles	Men: 62–106 µmol/L, Women: 44–80 µmol/L
eGFR	Estimated kidney filtering rate	Above 90 mL/min (normal)
Urea	Waste product from protein breakdown	2.5–7.8 mmol/L
Sodium	Salt balance	136–145 mmol/L
Potassium	Heart and muscle function	3.5–5.1 mmol/L

eGFR is the big one. It estimates how well your kidneys are working as a percentage of full function. Above 90 is normal. Between 60–89 might be fine if it's stable (it naturally decreases with age). Below 60 needs monitoring.

Creatinine is higher in people with more muscle mass. If you train regularly and your creatinine is slightly above range, mention this to your GP — it may not be a kidney problem at all.

Potassium is worth paying attention to because both high and low potassium can affect your heart rhythm. It's usually fine, but it's one of the results your GP will flag quickly if it's out of range.

Thyroid function tests

Thyroid tests check whether your thyroid gland is producing the right amount of hormones. An underactive or overactive thyroid affects your energy, weight, mood, and body temperature.

Marker	What It Measures	Normal UK Range
TSH (thyroid stimulating hormone)	Brain's signal to the thyroid	0.27–4.2 mIU/L
Free T4 (thyroxine)	Main thyroid hormone	12–22 pmol/L
Free T3 (triiodothyronine)	Active thyroid hormone	3.1–6.8 pmol/L

TSH is usually the first thing tested. If it's high, your thyroid is probably underactive (hypothyroidism) — your brain is shouting louder to get the thyroid to produce more. If it's low, your thyroid may be overactive (hyperthyroidism).

Most GPs test TSH first and only add T4 and T3 if TSH is abnormal. If you're paying for a private test, it's worth getting all three for the full picture. Some people have a normal TSH but low T3, which can still cause symptoms.

Thyroid issues are common in the UK — roughly 1 in 20 people have some form of thyroid disorder. Women are 5 to 10 times more likely to be affected than men.

HbA1c (diabetes marker)

HbA1c measures your average blood sugar over the past 2–3 months. It's the standard test for diagnosing and monitoring type 2 diabetes in the UK.

Result	What It Means
Below 42 mmol/mol	Normal
42–47 mmol/mol	Pre-diabetes (at risk)
48 mmol/mol or above	Diabetes range

Unlike a fasting glucose test, HbA1c isn't affected by what you ate that morning. It gives a much better picture of your long-term blood sugar control.

If you're in the pre-diabetes range (42–47 mmol/mol), that's actually useful information. It means you have time to make changes before things progress. Losing even 5–7% of your body weight and getting 150 minutes of moderate activity per week can bring HbA1c back into the normal range for many people.

Iron and ferritin

Iron studies tell you whether you have enough iron in your blood and in your stores.

Marker	What It Measures	Normal UK Range
Serum iron	Iron currently in blood	10–30 µmol/L
Ferritin	Iron stored in your body	Men: 30–400 µg/L, Women: 13–150 µg/L
Transferrin saturation	How much iron is being transported	20–50%
TIBC	Blood's capacity to carry iron	45–80 µmol/L

Ferritin is the most useful single marker. Think of it as your iron savings account. You can have normal haemoglobin but low ferritin, which means your stores are depleted and you'll eventually become anaemic if nothing changes.

Low ferritin is incredibly common, especially in women, vegetarians, and people who donate blood regularly. Symptoms include fatigue, brain fog, hair loss, and feeling cold all the time. If your ferritin is below 30 µg/L even though the lab range says 13 is "normal," many GPs will still consider treating it.

On the flip side, very high ferritin (above 500 µg/L) can indicate inflammation, infection, or less commonly, a genetic condition called haemochromatosis. Your GP will investigate further if it's significantly raised.

Vitamin D

Vitamin D deficiency is extremely common in the UK — roughly 1 in 5 adults have low levels, and it's even more prevalent among shift workers and people who spend most of their day indoors.

Result	What It Means
Above 50 nmol/L	Adequate
25–50 nmol/L	Insufficient
Below 25 nmol/L	Deficient

Symptoms of low vitamin D include fatigue, aches, low mood, and frequent infections. The NHS recommends everyone in the UK takes a 10 microgram (400 IU) supplement during autumn and winter. If you work shifts or rarely see daylight, supplementing year-round makes sense.

If your level is very low (below 25 nmol/L), your GP may prescribe a high-dose loading course before switching you to a maintenance dose. Over-the-counter supplements from Aldi or Boots typically cost £2–5 for several months' supply.

CRP (C-reactive protein)

CRP measures general inflammation in your body. It's a non-specific marker — it tells you something is going on, but not what.

Result	What It Means
Below 5 mg/L	Normal
5–10 mg/L	Mild inflammation
Above 10 mg/L	Significant inflammation, needs investigation

A raised CRP can be caused by infections, chronic conditions like rheumatoid arthritis, or even a hard gym session. It's often used alongside other tests to build a picture, not as a standalone diagnosis.

hs-CRP (high-sensitivity CRP) is a more precise version used to assess cardiovascular risk. A level below 1 mg/L is low risk, 1–3 mg/L is moderate, and above 3 mg/L is higher risk. Some private blood test services include this in their panels.

Reality check: one test is just one snapshot

Here's something the online health forums rarely mention: a single blood test is just one moment in time. We see people panicking on Reddit because their ALT is 2 points above the reference range, or their TSH is 0.1 outside normal. That's not how your GP interprets results.

What matters is the trend. A slightly raised cholesterol that's been stable for three years is very different from one that's jumped by 2 mmol/L in six months. A ferritin of 15 in someone who feels fine is different from a ferritin of 15 in someone who can barely get through a shift.

If your GP says "your results are fine" and you feel fine, they probably are fine. If your GP says "your results are fine" but you feel awful, push for a retest in 6–8 weeks or consider a private blood test that includes a wider panel.

How to get the most accurate results

A few practical things that make a real difference to your blood test accuracy:

Fast if asked to — usually 8–12 hours for cholesterol and glucose tests. Water is fine
Stay hydrated — dehydration concentrates your blood and can falsely raise some markers
Mention your medications — statins, the contraceptive pill, and even paracetamol can affect liver markers
Time of day matters — cortisol is highest in the morning, testosterone drops through the day, and iron levels fluctuate
Avoid heavy exercise the day before — it can temporarily raise liver enzymes and CRP
Be consistent — if you're tracking results over time, try to test at roughly the same time of day and under similar conditions

For shift workers, this is particularly tricky. If you've just finished a night shift, your cortisol and glucose levels may look different from someone tested mid-morning after a normal sleep. Mention your work pattern when you discuss results with your GP.

When to get tested privately

NHS blood tests are free but limited. Your GP will usually only test for things they suspect based on your symptoms. If you want a broader health MOT or you're tracking specific markers over time, a private blood test might be worth the money.

Private testing services like Medichecks, Thriva, and Forth offer comprehensive panels from around £39–99. Most use either a finger prick home kit or a venous draw at a local clinic.

We've compared the main UK services in detail — see our Medichecks vs Thriva vs Forth review for a full breakdown of prices, accuracy, and what you actually get.

Understanding your results letter

When your GP surgery sends results, they'll typically say one of three things:

"Normal — no action needed" — everything is within range
"Satisfactory — continue current management" — usually for people on medication (e.g., thyroid meds, statins)
"Abnormal — please book an appointment" — something needs discussing

If you get the third one, don't spiral. "Abnormal" in medical language just means "outside the reference range." It doesn't mean something is seriously wrong. It means your GP wants to talk it through, possibly retest, or investigate further.

You have the right to see your actual numbers, not just the GP's summary. Most practices now offer online access through the NHS App, where you can view your full results with reference ranges.

This article is for informational purposes only and is not a substitute for professional medical advice. Always consult your GP before making changes to your diet, exercise routine, or health management.

Sources & Further Reading

Frequently Asked Questions

What is a normal full blood count result in the UK?

A normal FBC shows haemoglobin between 130–170 g/L for men and 120–150 g/L for women, white blood cells between 4.0–11.0 x10⁹/L, and platelets between 150–400 x10⁹/L. If all three are in range, your blood cell production and immune function look healthy.

How long do blood test results take in the UK?

Most NHS blood test results come back within 1–5 working days. Routine tests like FBC and liver function are usually available within 48 hours. More specialist tests (thyroid antibodies, vitamin D) can take up to a week. Private tests typically return results within 2–5 working days.

Can I see my blood test results online in the UK?

Yes. Most GP practices now provide online access through the NHS App or their own patient portal. You can view your full results with reference ranges, not just the GP's summary. If your practice hasn't enabled this yet, you can request a printout from reception.

What does it mean if my blood test results are slightly abnormal?

A slightly out-of-range result on its own rarely indicates a serious problem. Dehydration, recent exercise, medications, stress, and even the time of day can shift your numbers. Your GP will look at the overall pattern, your symptoms, and whether the result is trending in the wrong direction before deciding on next steps.

Should I get a private blood test if my GP says everything is fine?

If you feel well and your GP is satisfied, there's usually no need. But if you have ongoing symptoms that aren't being investigated, or you want to track markers like vitamin D, ferritin, or thyroid function over time, a private test can fill the gaps. Comprehensive panels start from around £39 with services like Medichecks and Thriva.

Do I need to fast before a blood test?

It depends on what's being tested. Cholesterol and triglyceride tests usually require an 8–12 hour fast for the most accurate results. HbA1c, FBC, thyroid, and most other tests don't require fasting. Your GP or the testing service will tell you in advance. Drinking water is always fine.