Blood tests: what happens when you have one and what do they show?

Why will I have a blood test?

Blood tests are usually done to check how your body copes with illness, injury, inflammation, infection and some types of medicine.

There are many different types of blood test that look for different things in your blood. 

If your blood test results are not in normal levels, it gives doctors a good indication of how to treat you or prevent problems occurring in the future. 

Where would I have a blood test?

Blood tests can be done in various medical settings.

Some you can only have in hospital, like a troponin test, that tells doctors in an emergency what type of heart condition you have.

Others you have at your GP surgery. These are usually done to check on risk factors like high cholesterol and to monitor how a medicine is working.

Some pharmacies also offer blood tests as part of an NHS health check.

This check usually involves quick finger prick blood tests that looks at the blood’s glucose and cholesterol levels.

If the results are higher than recommended, you may be asked to go to your hospital for a full blood test.

• Go the NHS website to learn more about the NHS health check.

What is blood tested for?

Blood tests can be used to check many different things including: 

• Troponin - high levels of this protein in your blood can show your heart is damaged. It’s commonly tested if you’re suspected of having a heart attack. 
• B-type natriuretic peptide (BNP) - high levels of this hormone in your blood can used to help diagnose heart failure. 
• Cholesterol and blood sugar levels - these can help to monitor your risk of heart and circulatory diseases and diabetes, or how your condition is being managed. 
• International Normalised Ratio (INR) - this is a measure of how quickly your blood clots. It will be checked regularly if you’re taking a medicine to prevent blood clots such as warfarin to make sure that you’re prescribed the correct dose. 
• Liver and kidney tests – these look for different chemicals and proteins in your blood that can indicate how your liver or kidneys are working. 

Can I eat and drink before a blood test?

Occasionally you may need to fast (not eat) before your blood test, but your medical team will let you know if you have to do this. 

Unless you have been told not to, drink water before your test as if you’re dehydrated it can be more difficult to find the vein where the nurse or doctor will take your blood from. 

How will my blood be taken?

There are five simple steps to having a blood test: 

1. First, the person taking your blood tightly wraps a rubber strap called a tourniquet around your upper arm. This helps to bring the vein that runs inside your arm to the surface, so it’s easier to find. 
2. Then, they clean the skin around the vein with a sterile alcohol wipe. 
3. They will then insert a small needle into the vein. If your veins are fragile or difficult to find, sometimes a different type of needle called a ‘butterfly’ (because it has plastic ‘wings’ on either side) is inserted into a small vein in the back of your hand. 
4. They will then attach a small bottle and blood will flow into it. When the bottle is full, the person performing the blood test may remove the bottle and replace it with another bottle for a different test. Each bottle has a different coloured top to show which test it is for. 
5. Once all the bottles are full, the needle is removed and a piece of cotton wool or a plaster will be put where the blood was taken to catch any bleeding. Bleeding from a vein usually stops very quickly, but this may take a few minutes if you take medicine to prevent blood clots (anticoagulants). 

What happens to my blood after the test?

After the test, your blood will be taken away to be analysed.

Usually, the blood bottles contain small amounts of a chemical to stop your blood clotting in the tube, so it can be measured accurately in the lab.

Each bottle is labelled with your name, date of birth and hospital number, and the date and time of when the blood was taken.

The results will be sent to your medical team.

How long do blood test results take?

This partly depends on how urgent the test is. Tests done in hospitals are usually ‘urgent’ and the results will be sent to the medical team in a few hours.  

But most tests done at your GP surgery are ‘routine’, meaning there is no urgency, so it may take a few days to get the results. 

If the people reporting on the blood results see anything they are worried about, they will contact your medical team, and they will get in touch with you. 

Will I need other tests too?

Sometimes after seeing the results of your blood tests, your medical team may want to do other tests, such as a scan on your heart, or an ECG (electrocardiogram), which checks your heart rhythm. 

• Learn more about other common tests for heart conditions, including CT scans and echocardiogram. 

I am scared of having a blood test, what can I do?

Many people feel worried before having a blood test and it’s nothing to be ashamed of. Make sure to tell the person who’s doing your blood test that you feel anxious as this will help them look after you better.

You could also ask someone to come with you and distract you during the test. Some people also find that doing breathing exercises helps them relax. 

• Try our breathing exercises to relieve stress.

If you faint at the sight of blood, let the person giving you a blood test know beforehand, as you may be able to lie down during the test to stop this from happening. 

If you have a fear of needles, let your clinic know in advance as they might be able to order a cream that numbs the area where the needle goes in.   

You may need to apply the cream at home before the test for it to work properly. 

Unfortunately, there is no ‘needle-free’ way of obtaining blood. 

• Read more about dealing with a fear of needles.

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