Reading your blood test results: a plain-English guide to common markers

Full Blood Count (FBC)

The FBC measures the cells in your blood. It's the most commonly requested test and tells you about anaemia, infection, clotting and several rarer conditions.

• Haemoglobin (Hb): The oxygen-carrying protein in red blood cells. Reference ~130–170 g/L for men, ~120–150 for women. Low Hb is anaemia — by far the most common cause is iron deficiency. High Hb can be dehydration or, rarely, polycythaemia.
• Mean Cell Volume (MCV): Average red cell size. Low MCV (microcytic) typically means iron deficiency or thalassaemia trait. High MCV (macrocytic) suggests B12 or folate deficiency, alcohol, hypothyroidism or some medications.
• White Cell Count (WCC) and differential: Total white cells and the breakdown (neutrophils, lymphocytes, monocytes, eosinophils, basophils). Raised neutrophils typically suggest bacterial infection or inflammation; raised lymphocytes can be viral; raised eosinophils suggest allergy, parasites or some drug reactions.
• Platelets: Small cells that initiate clotting. Reference 150–400 × 10^9/L. Very low platelets (under 50) bleed; very high (over 600) clot.

Liver function tests (LFTs)

LFTs are a misnomer — they measure liver damage and capacity, not function per se. They include several enzymes that leak from damaged liver cells, plus a couple of true synthetic markers.

• ALT (alanine transaminase): The most specific marker for liver cell damage. Reference up to about 40 IU/L. Mildly raised (50–80) often means fatty liver, alcohol or some medications. Markedly raised (above 200) suggests hepatitis or significant injury.
• AST (aspartate transaminase): Less specific than ALT — also found in muscle and heart. Raised AST with normal ALT can indicate muscle injury or cardiac issues. Raised together with ALT (and ALT > AST) is typical of liver disease; ALT < AST suggests alcohol-related liver disease or advanced fibrosis.
• ALP (alkaline phosphatase): Raised in bile-duct obstruction and bone disease. Pregnancy and growing children naturally have higher ALP.
• GGT (gamma-glutamyl transferase): Raised by alcohol and bile-duct issues. Helps distinguish liver-source ALP from bone-source ALP.
• Bilirubin: The breakdown product of red cells. Raised in liver disease, bile duct obstruction, haemolysis, or Gilbert's syndrome (a benign genetic variant affecting ~5% of people).
• Albumin: The main protein the liver makes. Low albumin is a signal of advanced liver disease, malnutrition or chronic illness.

Kidney function (U&Es)

• Urea: Nitrogen waste from protein breakdown. Raised in dehydration, gut bleeding, high protein intake; low in liver disease.
• Creatinine: Muscle waste product cleared by the kidneys. Reference varies with muscle mass and age. Raised creatinine means reduced kidney clearance.
• eGFR (estimated Glomerular Filtration Rate): A calculation that turns creatinine into a kidney function estimate. Normal >90; mild reduction 60–89 is often age-related; moderate 30–59 needs monitoring; under 30 needs specialist input.
• Electrolytes (sodium, potassium): Sodium reflects fluid balance; potassium is critical for heart rhythm and is often affected by diuretics, ACE inhibitors and kidney function.

Lipid profile

The lipid panel tells you about cardiovascular risk, not just 'cholesterol'.

• Total cholesterol: Reference under 5.0 mmol/L. Not the most useful number on its own.
• HDL (high-density lipoprotein, 'good' cholesterol): Higher is better. Above 1.0 in men, 1.2 in women is the target.
• LDL (low-density lipoprotein, 'bad' cholesterol): Reference depends on cardiovascular risk; under 3.0 is the population target, under 2.0 for those with existing cardiovascular disease.
• Triglycerides: Fasting reference under 1.7. Raised triglycerides often track with insulin resistance and metabolic syndrome.
• Non-HDL cholesterol: Total cholesterol minus HDL. NICE prefers this over LDL for cardiovascular risk assessment. Target under 4.0 generally, under 2.5 for high-risk patients.

HbA1c (glycated haemoglobin)

HbA1c reflects average blood glucose over the previous 90 days. It's the gold standard for diabetes diagnosis and monitoring.

• Below 42 mmol/mol (6.0%): Normal.
• 42–47 mmol/mol (6.0–6.4%): Prediabetes — increased risk of progression to type 2 diabetes. NICE recommends lifestyle intervention and annual repeat.
• 48 mmol/mol and above (6.5%): Diabetes. NICE diagnostic threshold.

If you're starting Mounjaro or Wegovy, HbA1c is part of our baseline panel.

Thyroid function

• TSH (Thyroid-stimulating hormone): The pituitary signal that drives thyroid output. High TSH = underactive thyroid (the pituitary is shouting). Low TSH = overactive thyroid or central pituitary problem.
• Free T4: The main hormone produced by the thyroid. Low means hypothyroidism; high means hyperthyroidism.
• Free T3: The more active form. Sometimes measured if TSH and T4 don't fit the clinical picture.
• Anti-TPO and anti-thyroglobulin antibodies: Indicate autoimmune thyroid disease (Hashimoto's or Graves').

Iron studies

Iron status is more than just haemoglobin. The picture matters.

• Ferritin: The body's iron storage protein. Low ferritin (under 30 in most adults, under 50 in older adults) confirms iron deficiency even if Hb is still normal.
• Transferrin saturation: Percentage of the iron-transport protein that's carrying iron. Low in iron deficiency; high in iron overload.
• TIBC (total iron-binding capacity): Raised in iron deficiency, low in chronic disease.

Vitamin D and B12/folate

• Vitamin D (25-OH vitamin D): Reference depends on guidelines. Under 25 nmol/L is deficiency; 25–49 is insufficiency; 50–75 is adequate but borderline; 75+ is optimal. See our Manchester vitamin D guide.
• Serum B12: Reference roughly 180–900 pmol/L (lab-specific). Under 150 is deficiency; 150–250 is a grey zone where active B12 (holotranscobalamin) or methylmalonic acid (MMA) testing helps; over 250 is generally adequate.
• Folate: Often paired with B12 because deficiency presentations overlap. Reference 7–40 nmol/L.

See our B12 deficiency symptoms guide for clinical context.

CRP and ESR

Both are inflammation markers.

• CRP (C-reactive protein): Rises within hours of inflammation onset. Reference under 5 mg/L. Mildly raised (5–20) suggests low-grade or chronic inflammation; markedly raised (over 100) usually indicates significant infection or active inflammatory disease.
• ESR (erythrocyte sedimentation rate): Slower to rise and slower to fall than CRP. Useful in monitoring chronic inflammatory conditions.

What 'high' and 'low' actually mean

Reference ranges are typically set as the central 95% of a healthy population. This means 5% of perfectly healthy people fall outside the range by definition. A single 'high' or 'low' result, especially if marginal, often means nothing clinically. What matters is:

• How far outside the range
• The trend over time
• What other markers are doing
• Your clinical picture (symptoms, medications, comorbidities)

A 'high' bilirubin in an otherwise well 30-year-old with Gilbert's syndrome means nothing. A 'high' bilirubin in someone with fatigue, dark urine and abdominal pain means a great deal.

When to repeat and when to act

General principles: minor abnormalities (within 10–20% of the reference range, no symptoms) typically warrant a repeat in 3–6 months rather than immediate action. Moderate abnormalities should be reviewed by a clinician within a few weeks. Markedly abnormal results, or any result in the context of significant symptoms, warrant prompt clinical assessment.

Don't make medication changes based on results without discussing with the prescriber. Don't panic about borderline results before getting context. Don't ignore consistently abnormal trends just because each individual value is in range.

How we approach blood test interpretation at Trafford Clinic

We do private blood testing across Greater Manchester — Manchester city centre, Old Trafford, Salford, Salford Quays, Sale, Altrincham, Stretford, Chorlton, Rusholme, Eccles, Whalley Range, Firswood and Manchester city centre. We accredited UKAS labs, return results in 24–72 hours, and — importantly — we go through the results with you in plain English. Most providers email you a PDF and leave you to it. We don't.

For specific panels see pre-Mounjaro baseline panel and our B12 testing page.

How to book

Book a blood test at traffordclinic.co.uk/blood-tests or call 0161 258 6149. Empire Pharmacy is GPhC-registered (premises 1123966); Haroon Iqbal is an Independent Prescriber (reg. 2051093) with 26 years of pharmacy experience.

Related reading: Pre-Mounjaro baseline panel, Vitamin D in Manchester, B12 deficiency symptoms.