Blood Tests
Overview
A blood test is a simple procedure where a small sample of your blood is taken and checked in a laboratory. It can help find out how well your body is working, help diagnose illnesses, and show whether treatments are effective.
Key facts
- A blood test only needs a tiny amount of blood, usually taken from your arm.
- The test itself takes only a few minutes, and you can go home right after.
- Many blood tests do not need special preparation, though some require fasting beforehand.
Blood tests are extremely common. They are one of the most routine checks performed by doctors around the world.
Blood tests can be needed by anyone, at any age, for many reasons — from routine health checks to monitoring long-term conditions.
Symptoms
- Excessive bleeding from the needle site that continues after you have applied firm pressure for several minutes
- The area becomes unusually swollen, painful, and feels hot, which could be a sign of infection
- Difficulty breathing or swelling of your face or lips, which could mean a severe allergic reaction
- ⚠Large bruising that spreads and is very painful
- ⚠A fever or redness around the needle site
- ⚠Dizziness or fainting after your test that does not settle quickly
Common symptoms
- Unexplained tiredness or weakness
- Fevers or infections that keep coming back
- Unexpected weight loss or gain
- Persistent pain or unusual bruising
Symptoms in children
- Poor growth or slow weight gain
- Frequent infections
- Unusual paleness or fatigue
Symptoms in older adults
- Confusion or memory changes
- Falls or dizziness
- Loss of appetite or unexplained weight loss
Causes
Main causes
- To check your overall health as part of a routine check-up
- To help diagnose a condition when you have symptoms
- To monitor a long-term condition, like diabetes or high cholesterol
- To screen for risk factors, such as high cholesterol or diabetes
Risk factors
- Having a chronic condition that needs monitoring
- Taking medicines that require regular blood monitoring
- Having a family history of conditions like diabetes, heart disease, or anaemia
- Being of certain age groups, as doctors may recommend routine blood checks
When to see a doctor
See a doctor urgently if:
- Sudden, severe symptoms such as chest pain or difficulty breathing — call your local emergency number immediately
- Excessive bleeding or signs of a severe allergic reaction after a blood test
Book a routine appointment if:
- You have ongoing, mild symptoms such as tiredness or weight change
- It is time for a routine health check or screening
- You have a long-term condition and need regular monitoring
Diagnosis
Blood tests are done by taking a small sample of blood from a vein in your arm using a fine needle. The sample is sent to a laboratory, where machines and specialists measure different parts of your blood.
Tests that may be done
- Full blood count — checks red and white blood cells and platelets
- Blood glucose — checks sugar levels
- Cholesterol and lipid panel — checks fats in your blood
- Liver function tests — checks how well your liver is working
- Kidney function tests — checks how well your kidneys are working
What to expect at your appointment
The health worker will clean the area, place a needle in a vein, and collect a small amount of blood. It feels like a quick scratch. Afterwards, they will put a small dressing on the site. You may be asked to wait a few minutes or you may leave immediately. Results are usually ready within a day or two, depending on the test.
Treatment
Blood tests themselves are not treatment. The results help your doctor decide what, if any, treatment you need. Depending on the result, your doctor may recommend lifestyle changes, medication, or further tests.
Self-care at home
- Drink plenty of water before your appointment, unless your doctor said not to.
- Eat a normal meal before the test unless you have been told to fast (not eat) for the test.
- Wear clothing with loose sleeves so your arm is easy to reach.
- Tell the person taking blood if you feel faint or nervous.
Medical treatments
Any treatment you receive will depend on what your blood test results show. For example, abnormal cholesterol or blood sugar levels may be managed with lifestyle changes and sometimes medication. Your doctor will explain your results and agree a plan with you. Always take medicines exactly as prescribed.
When is surgery considered?
Blood tests themselves never require surgery. If your blood test reveals an underlying condition that needs surgical treatment, your doctor will discuss the options with you.
Living with this condition
If you need regular blood tests, try to keep a routine. Book them at times that suit you, and keep a record of your results so you can see your progress. It can help to bring a list of questions or have a friend with you.
Lifestyle tips
- Take simple steps to support good health, such as staying active and sleeping well.
- Try to have a balanced diet and stay hydrated.
- If you smoke, consider support to quit.
- Attend your scheduled blood tests and follow-up appointments.
Diet and exercise
For most blood tests you can eat and drink normally. If you are having a fasting blood test, you will be told not to eat for 8–12 hours beforehand. After the test, eat and drink as usual. Regular physical activity and healthy eating help keep your blood results in a good range.
Mental health and emotional wellbeing
It is normal to feel anxious about needles, blood tests, or the results. Tell your healthcare team how you feel. They can help distract you or use a smaller needle. You can also bring someone for support. If you are worried about results, try to focus on the fact that knowing your numbers helps you take action.
Prevention
Blood tests are not something to prevent — they are a way to stay healthy. You can help prevent health problems by attending screenings when offered and talking to your doctor about your risk factors.
Vaccines
Some blood tests check whether your body has immunity to certain diseases, for example after vaccination. Keeping your vaccinations up to date can help prevent infections that might otherwise show up in blood tests.
Screening programmes
Doctors often use blood tests as a screening tool to catch conditions early, like high cholesterol, diabetes, or anaemia. Ask your doctor how often you should have screening.
Complications
If left untreated
- If you avoid needed blood tests, underlying conditions such as diabetes, kidney disease, or anaemia might go unnoticed and worsen over time.
- Ignoring symptoms that prompted a blood test can delay diagnosis and treatment.
Long-term outlook
For almost everyone, blood tests are quick, safe, and painless. Most results are normal, and when they are not, knowing early gives you the best chance of managing your health.
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Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
Sources and guidance
Sources used for this article include the references listed below.
Last updated: October 20, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.
Guidance may differ by country or region. Confirm local recommendations with a qualified healthcare provider.