What Can a Blood Test Detect? A Complete UK Guide

How blood tests work — a 60-second primer

A blood sample — whether drawn from a vein at a clinic or collected via a finger-prick kit at home — is sent to a laboratory where automated analysers measure the concentration of specific substances. These substances fall into broad categories: cells (red, white, platelets), proteins and enzymes produced by organs, hormones secreted by glands, vitamins and minerals absorbed from food, metabolic waste products filtered by kidneys, and lipids circulating through your cardiovascular system.

Each measurement is compared against a reference range — a statistical band derived from a large sample of the general population. If your result falls outside this range, it may indicate a problem. But “in range” does not always mean “optimal”: reference ranges are designed to catch disease, not to tell you whether you're functioning at your best. That distinction matters, and we'll come back to it.

In the UK, most blood tests are processed in UKAS-accredited laboratories operating under ISO 15189 standards — the same accreditation whether you go through the NHS, a private clinic, or a home testing service.

What can a blood test detect? Blood cell disorders

A full blood count (FBC) is the single most commonly ordered blood test in the UK. It measures 15 parameters across three cell lines:

• Red blood cells (haemoglobin, haematocrit, MCV, MCH, MCHC): Low haemoglobin indicates anaemia — the most common blood disorder worldwide, affecting roughly 1.8 billion people globally. The mean cell volume (MCV) helps classify the type: microcytic (iron deficiency), normocytic (chronic disease), or macrocytic (B12/folate deficiency).
• White blood cells (total WBC + differential): Elevated white cells can signal infection, inflammation, allergic reactions, or in rare cases leukaemia. A low count (neutropenia) may indicate viral illness, autoimmune conditions, or medication side effects.
• Platelets: High platelets (thrombocytosis) raise clotting risk; low platelets (thrombocytopenia) raise bleeding risk. Both can be early markers of underlying conditions including bone marrow disorders.

The FBC is included in virtually every NHS blood test panel and every Helvy test. It's the foundation — cheap, fast, and remarkably informative.

Vitamin and mineral deficiencies

Deficiencies are far more common than most people realise. The National Diet and Nutrition Survey (NDNS) consistently shows that significant proportions of the UK adult population are below recommended levels for key micronutrients.

The NHS will check vitamin D and B12 if your GP suspects a deficiency, but rarely tests the full panel proactively. A comprehensive private blood test typically covers all of the above in a single draw. Read our full guide on vitamin deficiency blood tests.

Thyroid conditions

Your thyroid gland controls metabolism, energy and body temperature. Blood tests detect thyroid problems by measuring:

• TSH (thyroid-stimulating hormone): The first-line screening test. High TSH suggests hypothyroidism; low TSH suggests hyperthyroidism.
• Free T4 and Free T3: The active thyroid hormones. T4 is converted to T3 in peripheral tissues. Some people convert poorly — their TSH looks normal but free T3 is low, causing persistent symptoms.
• Thyroid antibodies (TPO, TgAb): Detect autoimmune thyroid disease (Hashimoto's, Graves'), which NICE NG145 estimates affects 2–5% of the UK population.

The NHS typically tests TSH only. If it's abnormal, FT4 is added. FT3 and antibodies are rarely checked at GP level, which means subclinical thyroid conditions can go undiagnosed for years. Our full thyroid blood test guide covers when the full panel matters.

Hormonal imbalances

Hormones regulate everything from energy and mood to body composition and fertility. Key hormones detectable by blood tests include:

• Testosterone (total and free): Total testosterone in men declines roughly 1–2% per year after age 30. Symptoms of low testosterone — fatigue, reduced muscle mass, low libido, brain fog — overlap with many other conditions, making blood testing essential for diagnosis. The NHS reference range is wide (8.64–29 nmol/L); many men with “normal” results at the lower end still have symptoms. See our testosterone blood test guide.
• Oestradiol, FSH, LH, progesterone: In women, these hormones fluctuate across the menstrual cycle and shift dramatically during perimenopause. Blood tests can help distinguish perimenopause from thyroid dysfunction, identify PCOS, and monitor fertility markers.
• Cortisol and DHEA-S: Chronic stress elevates cortisol, which suppresses immune function, disrupts sleep, and accelerates muscle breakdown. DHEA-S declines with age and acts as a counterbalance. The cortisol:DHEA-S ratio is a more useful clinical marker than cortisol alone. See our cortisol blood test guide.
• SHBG (sex hormone-binding globulin): Binds testosterone and oestradiol, affecting how much is biologically active. High SHBG can mask adequate total testosterone, causing symptoms despite “normal” levels.

Diabetes, prediabetes and metabolic health

Over 4.4 million people in the UK live with diabetes, and an estimated 850,000 more are undiagnosed. Blood tests detect diabetes and prediabetes through two key markers:

• HbA1c (glycated haemoglobin): Reflects your average blood sugar over the past 2–3 months. An HbA1c of 42–47 mmol/mol indicates prediabetes; ≥48 mmol/mol indicates diabetes. NICE NG28 recommends annual HbA1c screening for high-risk groups.
• Fasting insulin: Fasting insulin rises years before blood sugar becomes abnormal. It's the earliest detectable marker of insulin resistance — the metabolic dysfunction that precedes type 2 diabetes by a decade or more. The NHS does not routinely test fasting insulin; it's one of the strongest arguments for a comprehensive private blood test.

The landmark Diabetes Prevention Programme demonstrated that lifestyle changes can reduce type 2 diabetes risk by 58% in people with prediabetes. But you can't intervene if you don't know your numbers.

Cholesterol and cardiovascular risk

Cardiovascular disease kills roughly 170,000 people in the UK each year. A lipid panel blood test is one of the most important preventive tools available. The standard NHS lipid profile includes total cholesterol, LDL, HDL and triglycerides. But more advanced markers paint a clearer picture:

• ApoB (apolipoprotein B): ApoB counts the number of atherogenic particles in your blood — a better predictor of heart disease than LDL cholesterol alone. The European Society of Cardiology now recommends ApoB as a primary treatment target.
• Lp(a) — lipoprotein(a): Lp(a) is genetically determined and not responsive to statins. Elevated Lp(a) approximately doubles cardiovascular risk, yet the NHS does not routinely test it. One in five people has elevated Lp(a) and most never find out.
• hs-CRP (high-sensitivity C-reactive protein): hs-CRP measures vascular inflammation, which the American Heart Association recognises as an independent risk factor for cardiovascular events. Below 1 mg/L is low risk; above 3 mg/L is high risk.

Read our detailed cholesterol blood test guide for the full breakdown.

Liver damage and disease

Your liver processes everything you eat, drink and absorb. A liver function test (LFT) measures enzymes and proteins that reveal liver stress, inflammation or damage:

• ALT and AST: Enzymes released when liver cells are damaged. Elevated ALT is the most sensitive marker for liver inflammation — from alcohol, medications, fatty liver disease (NAFLD), or viral hepatitis.
• GGT (gamma-glutamyl transferase): Particularly sensitive to alcohol consumption and biliary obstruction. GGT combined with ALT helps distinguish alcoholic from non-alcoholic liver disease.
• Albumin and bilirubin: Measure the liver's synthetic function. Low albumin or high bilirubin can indicate chronic liver disease, cirrhosis, or Gilbert's syndrome (a harmless genetic variant affecting ~5% of the population).

Non-alcoholic fatty liver disease (NAFLD) now affects roughly 1 in 3 UK adults and is usually asymptomatic until advanced. Regular liver function testing is the only way to catch it early.

Kidney function and disease

Your kidneys filter ~180 litres of blood per day. Chronic kidney disease (CKD) affects approximately 1 in 10 UK adults and is usually silent until advanced stages. A kidney function test measures:

• Creatinine and eGFR: eGFR (estimated glomerular filtration rate) is calculated from creatinine and tells you how well your kidneys are filtering. Below 60 ml/min for three or more months defines CKD stage 3.
• Urea: A waste product of protein metabolism. Elevated urea alongside low eGFR confirms impaired kidney function.
• Electrolytes (sodium, potassium): Kidney dysfunction disrupts electrolyte balance. High potassium is a medical emergency; subtle shifts over time indicate declining function.

Our full kidney function test guide covers CKD staging, risk factors, and what your results mean.

Inflammation and autoimmune conditions

Chronic low-grade inflammation is increasingly recognised as a root driver of cardiovascular disease, type 2 diabetes, neurodegeneration and some cancers. Blood tests detect inflammation through:

• CRP and hs-CRP: Standard CRP detects acute infections and flares. High-sensitivity CRP (hs-CRP) measures the low-level chronic inflammation that drives long-term disease. The CANTOS trial published in the New England Journal of Medicine demonstrated that reducing inflammation independently reduces cardiovascular events.
• ESR (erythrocyte sedimentation rate): A non-specific but sensitive marker for systemic inflammation. Often used alongside CRP to investigate autoimmune conditions, infections or malignancy.
• Homocysteine: An amino acid linked to cardiovascular risk and cognitive decline when elevated. Often indicates B12, folate or B6 deficiency.

Read our full inflammation blood test guide for the seven evidence-based interventions ranked by effect size.

Cancer blood tests: tumour markers and the Galleri trial

This is the question driving the most public interest in 2026: can a blood test detect cancer? The answer is nuanced.

Traditional tumour markers

Several blood-based tumour markers have been used in clinical practice for decades. These include PSA (prostate-specific antigen), CA-125 (ovarian), CEA (colorectal), CA 19-9 (pancreatic), and AFP (liver). However, these markers are primarily used for monitoring known cancers — not for screening healthy people. They produce too many false positives and false negatives to be reliable standalone screening tools.

The Galleri multi-cancer early detection test

The Galleri test, developed by GRAIL, uses cell-free DNA (cfDNA) methylation patterns in the blood to screen for over 50 types of cancer before symptoms appear. The landmark NHS-Galleri trial enrolled 142,000 participants aged 50–77 across England — the world's first randomised controlled trial of a multi-cancer early detection (MCED) blood test.

Results published in February 2026 showed that annual Galleri screening plus standard screening achieved a four-fold improvement in overall cancer detection rate compared with standard screening alone. Critically, the test also reduced Stage IV (late-stage) diagnoses and increased Stage I–II (early-stage) detection of the 12 prespecified deadly cancers.

However, the trial's primary statistical endpoint was not met: the reduction in Stage III–IV cancers did not reach the prespecified threshold for statistical significance. This is an important distinction — the test showed real clinical benefit but fell short of the strict statistical bar required for NHS-wide rollout.

What this means for you

Galleri is not yet available through the NHS for routine screening and is currently only offered through private providers at significant cost (~£750–850). It is not a replacement for existing NHS screening programmes (breast, bowel, cervical, lung). If you are invited for NHS cancer screening, you should attend regardless.

Helvy does not currently offer the Galleri test. Our blood tests focus on the biomarkers you can act on: vitamin levels, hormones, organ function, metabolic health and cardiovascular risk markers. However, several of the markers we test — including full blood count, liver enzymes, ferritin and inflammatory markers — can flag abnormalities that warrant further investigation, including potential malignancy.

For more on this topic, see our dementia blood test guide, which covers the p-tau217 blood test for Alzheimer's detection — another emerging diagnostic breakthrough.

What the NHS checks vs what it misses

The NHS Health Check, offered every five years to adults aged 40–74, is designed to detect cardiovascular risk. It typically includes:

This isn't a criticism of the NHS — it's a public health system optimised for population-level screening on a limited budget. But if you want a complete picture of your health, a comprehensive blood test fills the gaps. Read our full NHS vs private blood test comparison.

How often should you get a blood test?

There's no single answer, but here are evidence-based guidelines:

• Baseline test (any age): Everyone should have at least one comprehensive blood test to establish their personal baseline. Without a baseline, isolated results have limited context.
• Annual testing: For adults over 30, annual blood testing allows you to track trends over time. A single “in range” result means less than a pattern showing your ferritin dropping 15% per year.
• Quarterly testing: If you're actively optimising (supplementation, training, medication changes), retesting every 3–4 months confirms whether interventions are working.

For a deeper dive, see our guide on blood test frequency.

What to do with your results

Numbers without context are useless. When you receive blood test results, here's the hierarchy of action:

1. Red flags first: Any result marked as critically high or low needs GP review immediately. This includes very high potassium, very low haemoglobin, extremely elevated liver enzymes, or abnormal white cell counts suggesting malignancy.
2. Out-of-range results: Discuss with a doctor. Some out-of-range results are clinically insignificant (e.g., slightly elevated bilirubin in Gilbert's syndrome); others require intervention.
3. In-range but suboptimal: This is where comprehensive testing adds the most value. A vitamin D level of 52 nmol/L is “in range” by NHS standards (above 25 nmol/L), but the Endocrine Society considers 75–150 nmol/L optimal. The gap between “not deficient” and “optimal” is where targeted supplementation makes the biggest difference.
4. Track over time: Isolated snapshots are useful; longitudinal trends are powerful. A ferritin of 40 µg/L might be fine — unless it was 90 last year and you're trending down.

Every Helvy blood test comes with results reviewed by a GMC-registered doctor, written in plain English, with clear explanations of what each marker means for you and what to do about it.