Blood Test Results Explained UK: Complete Guide
Medically reviewed content. Last updated: February 2026.
Key Takeaways
- Blood test results in the UK use reference ranges — values derived from 95% of the healthy population. A result inside the range is not always optimal, and a result outside is not always dangerous.
- This guide covers every major blood test panel: full blood count (FBC), liver function, kidney function, lipid panel, thyroid, diabetes markers, iron studies, vitamins, hormones, and inflammatory markers.
- Each section includes a summary table with normal UK ranges, what high and low results mean, and links to in-depth individual biomarker guides.
- Context matters: age, sex, hydration, medications, time of day, and recent exercise all affect blood test results. Never interpret a single marker in isolation.
- If any result is outside the reference range or you have symptoms, share your results with a healthcare professional for proper clinical interpretation.
- The Core Health 45 and Peak Insights 70 blood tests cover all the markers discussed in this guide — results in 2 working days, from home.
Contents
- Understanding Your Blood Test Report
- Complete Blood Count (FBC) Results
- Liver Function Test Results
- Kidney Function Results
- Lipid Panel / Cholesterol Results
- Thyroid Function Results
- Diabetes / Blood Sugar Results
- Iron Studies Results
- Vitamin Results
- Hormone Results
- Inflammatory Markers
- What to Do If Results Are Abnormal
- Frequently Asked Questions
Blood tests are the single most powerful tool in modern preventive health. A small sample of blood can reveal how well your organs are functioning, whether you are deficient in critical nutrients, how effectively your body is managing blood sugar and cholesterol, and whether silent inflammation or hormonal imbalances are affecting your health.
Yet for most people in the UK, receiving blood test results is a confusing experience. You get a list of abbreviations, numbers, and units you have never seen before — and often just a brief note from your GP saying everything is "normal." But what do those numbers actually mean? What counts as normal? And when should you be concerned?
This guide is your complete reference for understanding blood test results in the UK. We cover every major test panel, explain what each marker measures, provide the standard UK reference ranges, and explain what high or low results may indicate. Throughout the guide, we link to our detailed individual biomarker articles for deeper reading on any test that concerns you.
Whether you have just received NHS blood test results, had a private blood test through a service like Lola Health, or you are considering testing for the first time, this guide will help you understand exactly what your numbers mean.
Understanding Your Blood Test Report
Before diving into specific tests, it helps to understand how blood test results are structured in the UK. Every report, whether from the NHS or a private laboratory, follows a similar format.
Reference Ranges
Every biomarker on your blood test report comes with a reference range — the range of values considered normal for a healthy adult. These ranges are typically derived from the values found in 95% of the healthy population for that age and sex. If your result falls within the range, it is flagged as normal. If it falls outside, it is flagged as high or low.
Important caveats about reference ranges:
- Reference ranges vary between laboratories. Different UK labs may use slightly different ranges due to different testing methods, equipment, and population samples. Always use the range printed on your specific report.
- "Normal" does not always mean optimal. A ferritin of 15 µg/L may be technically within range but is associated with fatigue, hair loss, and poor exercise tolerance. Similarly, a vitamin D of 30 nmol/L is above the deficiency threshold but well below the 75–100 nmol/L range associated with best health outcomes.
- "Abnormal" does not always mean disease. A single result slightly outside the reference range may be due to dehydration, recent exercise, a heavy meal, or normal biological variation. Trends over time are far more meaningful than any single snapshot.
Common Units Used in UK Blood Tests
UK laboratories predominantly use SI (Système International) units, which differ from the conventional units used in the United States. You will commonly encounter:
- mmol/L — millimoles per litre (cholesterol, glucose, electrolytes)
- g/L — grams per litre (haemoglobin, albumin)
- µg/L or ng/mL — micrograms per litre (ferritin, vitamin B12)
- nmol/L — nanomoles per litre (vitamin D, hormones)
- pmol/L — picomoles per litre (Free T4, Free T3)
- mIU/L or mU/L — milli-international units per litre (TSH, insulin)
- U/L — units per litre (liver enzymes)
- 109/L — billions per litre (white blood cells, platelets)
- 1012/L — trillions per litre (red blood cells)
- fL — femtolitres (MCV — mean cell volume)
Flags: H, L, and Critical Values
Most blood test reports use simple flags next to your results:
- H or HIGH — your result is above the upper limit of the reference range
- L or LOW — your result is below the lower limit of the reference range
- No flag — your result is within the expected range
- Some laboratories use colour coding (red for abnormal, amber for borderline, green for normal) or asterisks (*) for values requiring attention
A result flagged as high or low is not, by itself, a diagnosis. It is a signal that further investigation or monitoring may be warranted — and context (your symptoms, medical history, medications, and trends over time) is essential for proper interpretation.
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Complete Blood Count (FBC) Results Explained
The full blood count (FBC), also called a complete blood count (CBC), is the most commonly ordered blood test in the UK. It measures the cellular components of your blood — red blood cells, white blood cells, and platelets — providing a broad overview of your general health, immune function, and oxygen-carrying capacity.
An FBC is included in virtually every standard blood test panel and is often the first test your GP will order when investigating symptoms such as fatigue, recurrent infections, bruising, or shortness of breath.
| Test | Normal Range (UK) | What High May Indicate | What Low May Indicate |
|---|---|---|---|
| White Blood Cells (WBC) | 4.0–11.0 × 109/L | Infection, inflammation, stress response, leukaemia (rare) | Viral infection, bone marrow suppression, autoimmune conditions |
| Red Blood Cells (RBC) | Men: 4.5–5.5 × 1012/L Women: 3.8–5.0 × 1012/L |
Polycythaemia, dehydration, chronic hypoxia, smoking | Anaemia, blood loss, bone marrow failure, nutritional deficiency |
| Haemoglobin (Hb) | Men: 130–170 g/L Women: 120–150 g/L |
Polycythaemia vera, chronic lung disease, dehydration | Iron-deficiency anaemia, B12/folate deficiency, chronic disease, blood loss |
| Platelets | 150–400 × 109/L | Reactive thrombocytosis (infection, inflammation), iron deficiency, myeloproliferative disorder | Viral infections, autoimmune destruction (ITP), bone marrow disorders, liver disease |
| MCV (Mean Cell Volume) | 80–100 fL | B12 or folate deficiency (macrocytic anaemia), alcohol excess, hypothyroidism, liver disease | Iron deficiency (microcytic anaemia), thalassaemia trait, chronic disease |
How to read your FBC results: The FBC is a screening tool, not a definitive diagnosis. If your haemoglobin is low, the MCV helps determine the likely cause — a low MCV points toward iron deficiency, while a high MCV suggests B12 or folate deficiency. If white blood cells are elevated, the differential count (neutrophils, lymphocytes, monocytes, eosinophils, basophils) helps distinguish between bacterial infection, viral infection, allergic reactions, and other causes.
For a comprehensive walkthrough of every FBC marker, read our full guide: Full Blood Count Explained.
Liver Function Test Results Explained
Liver function tests (LFTs) are among the most frequently ordered blood tests in the UK. Your liver performs over 500 essential functions — including detoxification, protein synthesis, bile production, and metabolism of fats, carbohydrates, and medications. LFTs provide a window into how well this critical organ is performing.
For a detailed explanation of all liver markers, see our complete guide: Understanding Liver Function Test Results.
| Test | Normal Range (UK) | What High May Indicate | What Low May Indicate |
|---|---|---|---|
| ALT (Alanine Aminotransferase) | Men: <41 U/L Women: <33 U/L |
Fatty liver disease (NAFLD/MASLD), hepatitis, alcohol damage, medication toxicity | Generally not clinically significant; very low levels are normal |
| AST (Aspartate Aminotransferase) | <40 U/L | Liver damage, muscle damage, heart attack, strenuous exercise | Generally not clinically significant |
| GGT (Gamma-GT) | Men: 10–71 U/L Women: 6–42 U/L |
Alcohol use, bile duct obstruction, fatty liver, metabolic syndrome, medications | Generally not clinically significant |
| ALP (Alkaline Phosphatase) | 30–130 U/L | Bile duct obstruction, bone disease (Paget's), vitamin D deficiency, pregnancy | Malnutrition, hypothyroidism, zinc deficiency (rare) |
| Bilirubin (Total) | <21 µmol/L | Gilbert's syndrome (benign, affects ~5% of UK population), liver disease, haemolysis, bile duct blockage | Generally not clinically significant |
| Albumin | 35–50 g/L | Dehydration (relative increase) | Chronic liver disease, malnutrition, kidney disease (nephrotic syndrome), inflammation |
Key patterns to understand: When ALT is the most elevated enzyme, the problem is likely within the liver cells themselves (hepatocellular damage). When ALP and GGT are elevated together with normal or mildly elevated ALT, this suggests a biliary (bile duct) problem. GGT elevated on its own is often associated with alcohol consumption, metabolic syndrome, or medications. An elevated bilirubin with otherwise normal liver enzymes is most commonly Gilbert's syndrome — a harmless genetic condition affecting roughly 5–8% of the UK population.
Fatty liver disease (NAFLD/MASLD) is now the most common liver condition in the UK, estimated to affect 1 in 3 adults. It is often detected through mildly elevated ALT and GGT on routine blood tests, and is strongly associated with insulin resistance, obesity, and elevated triglycerides.
Kidney Function Results Explained
Your kidneys filter approximately 180 litres of blood per day, removing waste products, regulating fluid balance, and maintaining electrolyte levels. Kidney function tests assess how efficiently your kidneys are performing these critical tasks. Chronic kidney disease (CKD) affects an estimated 7% of the UK adult population, yet the majority of early-stage CKD is asymptomatic — making blood testing essential for detection.
| Test | Normal Range (UK) | What High May Indicate | What Low May Indicate |
|---|---|---|---|
| Creatinine | Men: 59–104 µmol/L Women: 45–84 µmol/L |
Reduced kidney function, dehydration, high muscle mass, creatine supplementation | Low muscle mass, pregnancy, malnutrition |
| eGFR (Estimated Glomerular Filtration Rate) | >90 mL/min/1.73m² | Not typically flagged as high; very high eGFR is normal | 60–89: mild reduction; 30–59: moderate CKD; <30: severe CKD; <15: kidney failure |
| Urea | 2.5–7.8 mmol/L | Kidney dysfunction, dehydration, high-protein diet, gastrointestinal bleeding | Low-protein diet, severe liver disease, overhydration |
| Uric Acid | Men: 200–430 µmol/L Women: 140–360 µmol/L |
Gout risk, kidney stones, metabolic syndrome, kidney disease, high-purine diet | Low-purine diet, certain medications, Fanconi syndrome (rare) |
Understanding eGFR: The eGFR is the single most important kidney function marker. It is calculated from your creatinine result, adjusted for age and sex, and estimates how many millilitres of blood your kidneys filter per minute. An eGFR above 90 is normal. Between 60 and 89, there may be mild reduction — but this can be normal in older adults and does not necessarily indicate disease unless proteinuria (protein in urine) is also present. Below 60 is classified as chronic kidney disease and warrants monitoring and further investigation.
Important note: creatinine is affected by muscle mass. Very muscular individuals may have elevated creatinine (and therefore a lower eGFR) without any kidney dysfunction. Conversely, individuals with low muscle mass may have a "normal" creatinine that actually masks early kidney decline. If you are very muscular or have concerns about your eGFR result, a cystatin C blood test provides a more accurate estimate.
Lipid Panel / Cholesterol Results Explained
A lipid panel is essential for assessing your cardiovascular risk. Heart disease remains the leading cause of death in the UK, and elevated cholesterol is one of the most modifiable risk factors. Yet many people are confused by their cholesterol results — particularly the distinction between "good" and "bad" cholesterol. For a comprehensive overview, see our cholesterol level chart UK guide.
| Test | Desirable Level (UK) | What High May Indicate | What Low May Indicate |
|---|---|---|---|
| Total Cholesterol | <5.0 mmol/L | Increased cardiovascular risk, familial hypercholesterolaemia, hypothyroidism, diet | Malnutrition, hyperthyroidism, liver disease, statin therapy |
| LDL Cholesterol | <3.0 mmol/L (lower if high risk) |
Atherosclerosis risk, familial hypercholesterolaemia, saturated fat intake | Statin therapy, malabsorption, hyperthyroidism |
| HDL Cholesterol | Men: >1.0 mmol/L Women: >1.2 mmol/L |
Generally protective; very high levels (>2.3) may paradoxically increase risk | Increased cardiovascular risk, metabolic syndrome, smoking, sedentary lifestyle |
| Triglycerides | <1.7 mmol/L (fasting) | Metabolic syndrome, insulin resistance, high-sugar diet, alcohol, obesity, pancreatitis risk (>10) | Malnutrition, hyperthyroidism, malabsorption |
| Non-HDL Cholesterol | <4.0 mmol/L | All atherogenic lipoproteins elevated — considered better than LDL alone for risk assessment | Statin therapy, low-fat diet, malabsorption |
| ApoB (Apolipoprotein B) | <1.0 g/L (optimal <0.7 g/L) |
High number of atherogenic particles — the most accurate single marker for cardiovascular risk | Statin therapy, low cardiovascular risk |
Why ApoB matters: Traditional lipid panels measure the cholesterol content of lipoprotein particles. But what actually drives atherosclerosis is the number of atherogenic particles entering the artery wall — and each of these particles carries exactly one ApoB molecule. ApoB is therefore a direct count of atherogenic particles and is increasingly regarded by leading cardiologists and longevity physicians as the single best blood marker for cardiovascular risk.
The triglyceride-to-HDL ratio is another valuable metric you can calculate from your lipid panel. A ratio above 1.7 (in mmol/L units) suggests insulin resistance and metabolic syndrome, even when individual numbers appear normal. This ratio is particularly useful for identifying people at risk of type 2 diabetes and cardiovascular disease before conventional markers become abnormal.
Thyroid Function Results Explained
Your thyroid gland controls your metabolism, energy, mood, weight, and body temperature. Thyroid disorders affect approximately 1 in 20 people in the UK, with women up to 10 times more likely to be affected. For a complete deep-dive, see our thyroid blood test UK guide.
| Test | Normal Range (UK) | What High May Indicate | What Low May Indicate |
|---|---|---|---|
| TSH | 0.27–4.2 mIU/L | Hypothyroidism (underactive thyroid), Hashimoto's thyroiditis | Hyperthyroidism (overactive thyroid), Graves' disease |
| Free T4 | 12–22 pmol/L | Hyperthyroidism, levothyroxine overmedication | Hypothyroidism, pituitary dysfunction |
| Free T3 | 3.1–6.8 pmol/L | Hyperthyroidism, T3 thyrotoxicosis | Poor T4-to-T3 conversion, low T3 syndrome, selenium/zinc deficiency |
| TPO Antibodies | <34 kU/L | Hashimoto's thyroiditis (~95%), Graves' disease (~85%), autoimmune thyroid disease | Normal — low levels are expected in healthy individuals |
Why a full thyroid panel matters: Most NHS thyroid blood tests measure only TSH. While TSH is a useful first-line screening tool, it can appear normal in the early stages of Hashimoto's thyroiditis, during T4-to-T3 conversion problems, and in cases of pituitary dysfunction. Testing Free T4, Free T3, and TPO antibodies gives a far more complete picture. TPO antibodies, in particular, can be elevated for years before TSH becomes abnormal — acting as an early warning system for autoimmune thyroid disease.
Thyroid dysfunction is closely linked to nutritional deficiencies in vitamin D, iron, and vitamin B12. If your thyroid markers are borderline, testing these alongside is essential. Related reading: fatigue blood test UK, menopause blood test UK.
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Diabetes / Blood Sugar Results Explained
Diabetes and insulin resistance are among the most significant health challenges in the UK. An estimated 4.4 million people are living with type 2 diabetes, and a further 2.4 million are at high risk of developing it. Blood sugar markers are critical for early detection — because by the time fasting glucose becomes abnormal, insulin resistance has often been present for years.
| Test | Normal Range (UK) | What High May Indicate | What Low May Indicate |
|---|---|---|---|
| HbA1c | <42 mmol/mol (normal) 42–47: pre-diabetes ≥48: diabetes |
Pre-diabetes, type 2 diabetes, poor glycaemic control | Hypoglycaemia, recent blood loss, haemoglobin variants, haemolytic anaemia |
| Fasting Glucose | 3.9–5.5 mmol/L 5.6–6.9: impaired ≥7.0: diabetes |
Impaired fasting glucose, diabetes, stress, Cushing's syndrome, medications (steroids) | Reactive hypoglycaemia, excess insulin, adrenal insufficiency, liver disease |
| Fasting Insulin | 2–13 mU/L (optimal <8 mU/L) |
Insulin resistance, early type 2 diabetes risk, PCOS, metabolic syndrome | Type 1 diabetes, late-stage beta cell failure, pancreatic disease |
Why HbA1c is the gold standard: Unlike fasting glucose, which gives a single point-in-time measurement and can be affected by stress, sleep, and recent meals, HbA1c reflects your average blood sugar over the previous 2–3 months. It measures the percentage of haemoglobin that has become glycated (bonded to glucose). This makes it far more reliable for detecting developing diabetes and monitoring long-term glucose control.
The case for fasting insulin: Fasting insulin is arguably the earliest marker of metabolic dysfunction. Your body can maintain normal blood glucose for years by producing ever-increasing amounts of insulin. By the time glucose or HbA1c become abnormal, insulin resistance may have been present for a decade. Testing fasting insulin gives you a much earlier warning. Related reading: PCOS blood test, weight loss blood test.
Iron Studies Results Explained
Iron deficiency is the most common nutritional deficiency worldwide and is particularly prevalent in the UK, affecting an estimated 31.6% of women. Yet iron status is often poorly assessed — many GPs check only haemoglobin and declare iron levels "normal" even when ferritin (iron stores) is dangerously low. For a full overview, see our guides to normal iron levels and normal ferritin range UK.
| Test | Normal Range (UK) | What High May Indicate | What Low May Indicate |
|---|---|---|---|
| Ferritin | Men: 30–400 µg/L Women: 13–150 µg/L (optimal >50 µg/L) |
Iron overload (haemochromatosis), inflammation (acute phase reactant), liver disease, infection | Iron depletion, iron-deficiency anaemia, heavy menstruation, coeliac disease, blood loss |
| Serum Iron | 10–30 µmol/L | Haemochromatosis, iron supplementation, haemolytic anaemia, liver disease | Iron deficiency, chronic disease, inflammation, poor dietary intake |
| TIBC (Total Iron Binding Capacity) | 45–72 µmol/L | Iron deficiency (body increases binding capacity to capture more iron), pregnancy | Iron overload, chronic disease, inflammation, malnutrition, liver disease |
| Transferrin Saturation | 20–50% | Haemochromatosis (>45% warrants investigation), iron overload | Iron deficiency (<16% strongly suggestive), chronic disease |
The ferritin trap: One of the most important things to understand about iron testing is that a "normal" ferritin does not always mean adequate iron. Most UK labs use a lower reference limit of around 13–15 µg/L for women, but research consistently shows that symptoms of iron deficiency — fatigue, hair loss, poor exercise tolerance, restless legs — improve when ferritin is raised above 50 µg/L. If your ferritin is 20 and your GP says it is "normal," it may still be the cause of your symptoms.
Ferritin is also an acute phase reactant, meaning it rises during inflammation and infection. If your ferritin appears normal or high but you have symptoms of iron deficiency, checking transferrin saturation and TIBC can reveal whether iron deficiency is being masked by an inflammatory state. Related reading: fatigue blood test, hair loss blood test.
Vitamin Results Explained
Vitamin deficiencies are remarkably common in the UK, often causing symptoms that overlap with other conditions. Testing vitamin levels is essential for anyone experiencing fatigue, low mood, muscle weakness, brain fog, or recurrent illness.
| Test | Normal Range (UK) | What High May Indicate | What Low May Indicate |
|---|---|---|---|
| Vitamin D (25-OH) | >50 nmol/L (sufficient) 75–150 nmol/L (optimal) <25 nmol/L (deficient) |
Excessive supplementation (>250 nmol/L may cause toxicity, though rare) | Bone pain, muscle weakness, fatigue, low mood, impaired immunity, increased fracture risk |
| Vitamin B12 | 190–900 ng/L (optimal >400 ng/L) |
Supplementation (excess is excreted; rarely clinically significant) | Pernicious anaemia, vegan/vegetarian diet, malabsorption, macrocytic anaemia, neurological symptoms |
| Folate | >3.9 µg/L | Supplementation or high dietary intake (folic acid fortified foods) | Macrocytic anaemia, neural tube defect risk (pregnancy), poor diet, coeliac disease, alcohol |
Vitamin D in the UK: The UK's northern latitude (above 50°N) means that between October and March, UVB sunlight is insufficient for vitamin D synthesis. Public Health England estimates that 1 in 5 people in the UK have vitamin D levels below 25 nmol/L (deficient), and a much larger proportion fall below the 75 nmol/L threshold associated with optimal health. Supplementation of at least 400 IU (10 µg) daily is officially recommended for all UK adults during winter, though many experts and the Endocrine Society suggest 1,000–2,000 IU daily is more appropriate, particularly for those with confirmed deficiency.
B12 and folate: These work together in red blood cell production and nervous system function. Deficiency in either causes macrocytic anaemia (large, immature red blood cells), visible on an FBC as elevated MCV. B12 deficiency is particularly common in vegans and vegetarians (B12 is found almost exclusively in animal products), people over 50 (reduced stomach acid impairs absorption), and those with coeliac disease or other malabsorption conditions. Related reading: vegan blood test UK, brain fog blood test.
Hormone Results Explained
Hormones are chemical messengers that regulate growth, metabolism, reproduction, mood, and energy. Hormonal imbalances are a common cause of fatigue, weight changes, mood disturbances, and reproductive problems. For detailed guides, see our articles on testosterone blood test, oestrogen blood test, and cortisol blood test.
| Test | Normal Range (UK) | What High May Indicate | What Low May Indicate |
|---|---|---|---|
| Testosterone | Men: 8.6–29 nmol/L Women: 0.3–1.7 nmol/L |
Men: exogenous testosterone/anabolic steroids. Women: PCOS, adrenal tumour | Hypogonadism, ageing, obesity, pituitary dysfunction, chronic illness, opioid use |
| Oestradiol (E2) | Women (varies by cycle phase): Follicular: 46–607 pmol/L Ovulatory: 315–1828 pmol/L Luteal: 161–774 pmol/L Postmenopausal: <183 pmol/L Men: 40–161 pmol/L |
Oestrogen-producing tumour, obesity (aromatase activity), liver disease, HRT | Menopause, perimenopause, premature ovarian insufficiency, excessive exercise, low body weight |
| FSH (Follicle-Stimulating Hormone) | Women: varies by cycle Postmenopausal: >25.8 IU/L Men: 1.5–12.4 IU/L |
Menopause/perimenopause (in women), primary gonadal failure, premature ovarian insufficiency | Pituitary dysfunction, polycystic ovary syndrome, hypothalamic amenorrhoea |
| LH (Luteinising Hormone) | Women: varies by cycle Postmenopausal: 7.7–58.5 IU/L Men: 1.7–8.6 IU/L |
Menopause, PCOS (when LH:FSH ratio >2:1), primary gonadal failure | Pituitary dysfunction, hypothalamic amenorrhoea, anorexia |
| DHEA-S | Age-dependent Women 20–29: 2.7–9.2 µmol/L Men 20–29: 5.7–13.4 µmol/L (declines ~2% per year from age 30) |
Adrenal tumour, congenital adrenal hyperplasia, PCOS | Adrenal insufficiency, ageing, chronic stress, long-term steroid use |
| Cortisol | Morning (9AM): 166–507 nmol/L (varies by time of day) |
Cushing's syndrome, chronic stress, steroid medication, depression, alcohol excess | Addison's disease, adrenal insufficiency, pituitary dysfunction |
Interpreting hormone results requires context: Female hormone levels (oestradiol, FSH, LH, progesterone) vary dramatically across the menstrual cycle. Results must be interpreted in the context of when in the cycle the blood was drawn. For fertility investigations, day 2–5 of the cycle is standard for FSH and oestradiol. For progesterone (ovulation confirmation), day 21 is standard. Testosterone should ideally be measured before 10AM, as levels peak in the morning and decline throughout the day.
Related reading: menopause blood test UK, perimenopause blood test, fertility blood test UK, low testosterone symptoms, TRT blood tests UK.
Inflammatory Markers Explained
Chronic low-grade inflammation is increasingly recognised as a driver of cardiovascular disease, type 2 diabetes, cancer, and neurodegenerative conditions. Measuring inflammatory markers can reveal hidden inflammation that may not produce obvious symptoms but is silently damaging your health.
| Test | Normal Range (UK) | What High May Indicate | What Low May Indicate |
|---|---|---|---|
| hsCRP (High-Sensitivity C-Reactive Protein) | <1.0 mg/L: low risk 1.0–3.0 mg/L: moderate risk >3.0 mg/L: high risk >10 mg/L: acute infection/inflammation |
Cardiovascular risk, chronic inflammation, infection, autoimmune disease, metabolic syndrome, obesity | Low inflammatory state — generally desirable |
| ESR (Erythrocyte Sedimentation Rate) | Men: <age/2 mm/hr Women: <(age+10)/2 mm/hr (approx. guides) |
Infection, autoimmune disease (rheumatoid arthritis, lupus), polymyalgia rheumatica, malignancy, temporal arteritis | Polycythaemia, sickle cell disease (rarely clinically relevant) |
hsCRP and cardiovascular risk: Standard CRP tests measure inflammation broadly and are useful for detecting acute infections. The high-sensitivity version (hsCRP) measures much lower levels and is specifically validated as an independent risk factor for cardiovascular events. The American Heart Association classifies cardiovascular risk as: <1.0 mg/L (low risk), 1.0–3.0 mg/L (moderate risk), and >3.0 mg/L (high risk). However, an hsCRP above 10 mg/L usually indicates an acute infection or inflammatory process and should not be used for cardiovascular risk assessment until the acute cause has resolved.
ESR vs hsCRP: ESR is a less specific but useful marker that rises more slowly and stays elevated longer than CRP. It is particularly useful in monitoring chronic conditions such as rheumatoid arthritis, polymyalgia rheumatica, and temporal arteritis. The two markers complement each other — hsCRP is better for cardiovascular risk and acute changes, while ESR is better for monitoring chronic inflammatory conditions.
What to Do If Your Blood Test Results Are Abnormal
Receiving an abnormal blood test result can be alarming, but it is important to stay measured. Here is a practical framework for interpreting and acting on your results:
1. Do Not Panic Over a Single Abnormal Result
A single result slightly outside the reference range is extremely common and often not clinically significant. Reference ranges capture 95% of the healthy population — meaning 5% of perfectly healthy people will have at least one result outside the range on any given blood test. Temporary factors such as dehydration, recent exercise, stress, alcohol intake, or medications can shift results in either direction.
2. Look at Patterns, Not Isolated Numbers
Blood test results are most meaningful when interpreted as a group. For example, elevated ALT alongside elevated GGT and high triglycerides suggests metabolic fatty liver disease. Low ferritin with low MCV and low haemoglobin points strongly toward iron-deficiency anaemia. A single elevated marker with everything else normal is often less concerning than multiple borderline results pointing in the same direction.
3. Compare with Previous Results
Trends over time are far more informative than any single test. A ferritin of 40 µg/L is concerning if it was 120 µg/L six months ago, but reassuring if it was 15 µg/L six months ago. This is one of the most powerful reasons to test regularly — you build your own personal baseline.
4. Consider Your Symptoms and Context
An abnormal result that correlates with your symptoms is more significant than one that does not. A low Free T3 in someone with classic hypothyroid symptoms (fatigue, weight gain, cold intolerance) warrants further investigation, even if TSH is "normal." Conversely, a mildly elevated bilirubin in someone with no symptoms is almost certainly Gilbert's syndrome and rarely warrants concern.
5. Share Your Results with a Healthcare Professional
While this guide helps you understand what your results mean, blood test interpretation requires clinical context — your medical history, family history, medications, symptoms, and physical examination all inform the picture. If any result is significantly outside the reference range, or if you have symptoms that concern you, share your results with your GP or a private healthcare provider for proper clinical assessment.
6. Retest Before Drawing Conclusions
If a result is unexpectedly abnormal and you feel well, consider retesting in 4–6 weeks before pursuing invasive investigations. Many borderline results normalise on repeat testing. However, very abnormal results (e.g., haemoglobin significantly below range, very high liver enzymes, critically abnormal kidney function) should be discussed with a doctor promptly rather than waiting to retest.
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Frequently Asked Questions
What does "within normal range" mean on a blood test?
A result marked "within normal range" (or "within reference range") means your value falls within the interval that captures 95% of the healthy population. It does not necessarily mean your result is optimal for you personally. For example, a ferritin of 15 µg/L is within range at many UK labs but is associated with fatigue and iron depletion. Similarly, a vitamin D of 30 nmol/L is above the deficiency threshold but well below optimal. Context, symptoms, and trends over time all matter more than a simple in-range/out-of-range flag.
Why are my blood test results different from last time?
Blood test results naturally fluctuate. Factors that can cause variation between tests include hydration levels, time of day (cortisol and testosterone are highest in the morning), recent exercise (can elevate liver enzymes and creatine kinase), recent meals (affects glucose and triglycerides), alcohol intake, stress, menstrual cycle phase, medications, and even seasonal changes (vitamin D is typically lowest in February–March). Small fluctuations within the reference range are normal. Significant or persistent changes warrant further investigation.
How often should I get blood tests done?
For healthy adults with no known conditions, annual blood testing provides a good baseline. If you have a chronic condition (diabetes, thyroid disease, kidney disease), more frequent testing every 3–6 months is typical. If you are actively making lifestyle changes (diet, exercise, supplements) or have recently started medication, retesting after 8–12 weeks helps you track the impact. Regular testing is particularly valuable because it allows you to spot trends before problems develop.
Can I get a blood test without seeing my GP?
Yes. Private blood testing services in the UK allow you to order blood tests directly, without a GP referral or appointment. Services like Lola Health offer comprehensive panels with a professional phlebotomist visit at your home, workplace, or chosen location. Results are typically available within 2 working days. This is particularly useful for tests your GP may not routinely order, such as fasting insulin, ApoB, Free T3, or a full iron panel.
What is the difference between a finger-prick test and a venous blood test?
Finger-prick tests use a small lancet to collect a few drops of blood from your fingertip. They are convenient but have limitations: small sample volumes increase the risk of haemolysis (damage to blood cells), which can affect results for markers like potassium, LDH, and certain hormones. Some markers simply require more blood than a finger prick can reliably provide. A venous blood draw, taken from a vein in your arm by a trained phlebotomist, provides a larger, cleaner sample and is the gold standard for accuracy. For comprehensive panels testing 45–70+ markers, a venous draw is strongly recommended.
What blood tests should I ask my GP for?
At minimum, a useful annual check-up should include: FBC, liver function, kidney function (creatinine, eGFR), lipid panel, HbA1c, thyroid function (ideally full panel), ferritin, vitamin D, and vitamin B12. For a more comprehensive assessment, consider adding ApoB, fasting insulin, hsCRP, and a full iron panel. GPs may not routinely order all of these — private testing fills the gap.
Do I need to fast before a blood test?
Fasting is required for accurate triglyceride and fasting glucose results — typically 10–12 hours overnight (water is fine). HbA1c, FBC, liver function, kidney function, thyroid markers, vitamins, and most hormones do not require fasting. If your blood test includes a lipid panel or glucose, fasting is recommended for the most accurate results. If in doubt, fast — it will not affect non-fasting markers.
What does an HbA1c of 42–47 mmol/mol mean?
An HbA1c between 42 and 47 mmol/mol indicates pre-diabetes (also called non-diabetic hyperglycaemia). This means your average blood sugar over the past 2–3 months is higher than normal but not yet in the diabetic range (≥48 mmol/mol). Pre-diabetes is reversible through lifestyle changes — regular exercise, dietary modification (reducing refined carbohydrates and sugar), weight management, and improved sleep can all lower HbA1c. Without intervention, approximately 5–10% of people with pre-diabetes progress to type 2 diabetes each year.
What is the best blood test to get in the UK?
The "best" blood test depends on your goals. For a general health check, a comprehensive panel covering 45+ biomarkers (FBC, liver, kidney, lipids, thyroid, iron, vitamins, HbA1c, and inflammation) provides the broadest insight. The Core Health 45 covers exactly this. For a more advanced assessment including hormones, ApoB, fasting insulin, and additional markers, the Peak Insights 70 is the most comprehensive option available. Both include a professional phlebotomist visit at home and results within 2 working days. For specific concerns, see our guides on fatigue, thyroid, menopause, PCOS, and fertility blood tests.
How do I read blood test results from the NHS?
NHS blood test results are typically accessed through the NHS App or provided by your GP. Each result shows the biomarker name, your value, the reference range, and a flag (normal, high, or low). Results flagged as high (H) or low (L) fall outside the expected range and may require follow-up. If you only see a few markers (often just FBC and basic biochemistry), this is because GPs typically order a limited panel. For a more comprehensive picture, consider supplementing NHS tests with a private blood test that covers a wider range of biomarkers.
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→45-70 biomarkers tested · Venous blood draw · From £130