Blood test
Blood Test
A blood test involves taking a small sample of blood, usually from the arm, to check your health. Different tests look at blood cells, organs, sugar, cholesterol, hormones and more.
Quick answer
Blood Test: what it is and what the results mean
A blood test is one of the most common medical investigations. A small sample of blood is sent to a laboratory, where it can be analysed in dozens of ways depending on what the doctor is looking for.
- Why it is done: Blood tests help diagnose conditions, check how organs like the liver and kidneys are working, monitor long-term conditions and medicines, check for infection or inflammation, and screen for problems before they cause symptoms.
- Understanding results: Results are compared with a normal "reference range".
What it is
A blood test is one of the most common medical investigations. A small sample of blood is sent to a laboratory, where it can be analysed in dozens of ways depending on what the doctor is looking for.
Why it is done
Blood tests help diagnose conditions, check how organs like the liver and kidneys are working, monitor long-term conditions and medicines, check for infection or inflammation, and screen for problems before they cause symptoms.
What to expect
A healthcare professional usually takes blood from a vein in the arm using a small needle; it takes a minute or two. Some tests need you to fast (not eat) beforehand — you will be told if so. Afterwards there may be minor bruising.
Understanding the results
Results are compared with a normal "reference range". A result slightly outside the range is not always a problem, and results are always interpreted alongside your symptoms and history. Your clinician will explain what yours mean.
Good to know
Risks and limitations
Blood tests are very safe; the main effects are brief discomfort and occasional bruising or lightheadedness. No single blood test diagnoses everything — they are one piece of the picture.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
Blood Test: frequently asked questions
Do I need to fast before a blood test?
Only some tests (such as certain cholesterol or glucose tests) need fasting. You will be told in advance if you need to avoid eating beforehand.
What can a blood test show?
Depending on the test, blood can reveal anaemia, infection, inflammation, how the liver, kidneys and thyroid are working, blood sugar, cholesterol, hormone levels and much more.
Related tests
Other blood test investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Royal College of Radiologists / relevant professional body
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