Understand Your Blood Test Results
Enter your values for a personalised explanation, or work through each panel to learn how to read blood tests from scratch. Free, no signup, works on any device.
Full Blood Count(FBC)
A Full Blood Count measures the different types of cells in your blood: red blood cells that carry oxygen, white blood cells that fight infection, and platelets that help with clotting. It is one of the most commonly ordered blood tests in the UK.
The protein in red blood cells that carries oxygen around the body.
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Haemoglobin is the first marker most clinicians look at on an FBC. A level below 100 g/L is moderately severe anaemia; below 80 g/L is severe and may require transfusion depending on the clinical picture.
💬 Ask your clinician:
“My haemoglobin is low — could iron deficiency be the cause, and should I take a supplement?”
The average size of your red blood cells.
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MCV is the key discriminating marker for anaemia type. Low MCV with low Hb points to iron deficiency or thalassaemia. High MCV with low Hb points to B12 or folate deficiency. Normal MCV with low Hb is normocytic anaemia, seen in chronic disease, acute blood loss, or haemolysis.
💬 Ask your clinician:
“My MCV is low — is this likely to be iron deficiency and what should I do next?”
The total number of white blood cells in your blood, which form your immune system's response to infection and disease.
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The WBC differential is more informative than the total count alone. A raised neutrophil count within a raised WBC strongly suggests bacterial infection. A raised lymphocyte count suggests viral infection or CLL in older adults.
💬 Ask your clinician:
“My white blood cell count is low — are any of my regular medications likely to be the cause?”
Small cell fragments in your blood that clump together at sites of injury to form a clot and stop bleeding.
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An isolated raised platelet count with no other abnormality most commonly indicates iron deficiency or a reactive process. An isolated low count in an otherwise well patient most commonly indicates ITP.
💬 Ask your clinician:
“My platelets are low — is this likely to improve on its own, or does it need treatment?”
The most abundant white blood cell, forming the first line of defence against bacterial infections.
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Any patient on carbimazole or other myelosuppressive drugs who presents with a sore throat or fever should have an urgent FBC to check neutrophil count — agranulocytosis is a serious and potentially fatal adverse effect.
💬 Ask your clinician:
“My neutrophils are low — should I be taking any precautions to avoid infection?”
White blood cells involved in adaptive immunity, producing antibodies and coordinating the body's response to viral infections.
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In older adults, a persistent lymphocytosis is the most common presentation of CLL. CLL is often an incidental finding and many patients never require treatment, but it needs haematology follow-up.
💬 Ask your clinician:
“My lymphocytes have been persistently high on two separate blood tests — should this be investigated further?”
The total number of red blood cells per litre of blood.
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RBC is rarely interpreted in isolation. Its main value is in combination with Hb, MCV, and haematocrit to characterise anaemia or polycythaemia.
💬 Ask your clinician:
“My red blood cell count is low — what is the most likely cause given my other results?”
Common blood test questions
What does low haemoglobin mean?▾
A low haemoglobin is called anaemia. The most common cause in the UK is iron deficiency, often from poor dietary intake or blood loss. Looking at your MCV (red blood cell size) alongside haemoglobin helps identify the type — a low MCV points to iron deficiency, while a high MCV points to B12 or folate deficiency.
What is a normal TSH level in the UK?▾
The normal range for TSH (thyroid stimulating hormone) in UK laboratories is typically 0.4 to 4.5 mU/L. A raised TSH indicates an underactive thyroid (hypothyroidism). A suppressed TSH indicates an overactive thyroid (hyperthyroidism) or over-treatment with levothyroxine.
What does a raised ALT mean on a liver function test?▾
ALT (alanine aminotransferase) is the most sensitive marker of liver cell damage. A mildly raised ALT (up to three times the upper limit) is common with fatty liver disease, alcohol intake, and certain medications such as statins. A raised ALT alongside a raised GGT in a patient who drinks alcohol is the classic pattern of alcoholic liver disease.
What is HbA1c and what level means I have diabetes?▾
HbA1c measures your average blood glucose level over the previous 2 to 3 months. An HbA1c of 48 mmol/mol (6.5%) or above on two separate tests confirms a diagnosis of type 2 diabetes. A reading of 42 to 47 mmol/mol (6.0 to 6.4%) indicates prediabetes.
What does a low eGFR mean on a kidney function test?▾
eGFR (estimated glomerular filtration rate) measures how well your kidneys are filtering your blood. A normal eGFR is above 60 mL/min/1.73m². An eGFR below 60 on two occasions at least 90 days apart defines chronic kidney disease (CKD). The lower the eGFR, the more advanced the CKD.
What is LDL cholesterol and what level is too high?▾
LDL (low-density lipoprotein) is often called 'bad cholesterol' because it deposits cholesterol in artery walls. For most people, an LDL above 3.0 mmol/L warrants consideration of lifestyle changes or statin therapy based on overall cardiovascular risk. For people who have had a heart attack or stroke, the target is below 1.4 mmol/L.
What does low ferritin mean?▾
Ferritin is the main storage protein for iron. A ferritin below 30 µg/L indicates depleted iron stores, even if your haemoglobin is still normal. Below 15 µg/L confirms iron deficiency. Symptoms such as fatigue and brain fog can occur even before anaemia develops.
What does a high GGT mean on a liver function test?▾
GGT (gamma-glutamyl transferase) is the most sensitive marker of alcohol-related liver changes. It can be elevated by regular alcohol intake even before any structural liver damage occurs. GGT also rises with biliary obstruction and is used to confirm whether a raised ALP is from the liver or from bone.