What is a blood test?
A blood test is when a small sample of your blood is taken for testing in a laboratory.
Your doctor, a nurse or sometimes a phlebotomist (who is trained to take blood samples) will do the test. You may have your blood test at the hospital or at your local GP clinic.
How is the blood taken?
Your blood will be taken through a needle which is inserted through your skin into a vein. The most common places to take blood are from a vein inside your elbow or a vein on the back of your hand as your veins are closer to the surface there.
A tight band (tourniquet) is placed around your arm just above the area where the blood is to be taken. This causes the vein to come nearer to the surface of your skin, making it easier for your blood sample to be taken. The area will be cleaned with an antiseptic wipe or swab before the test is taken.
The needle is usually attached to a syringe or a plastic device called a vacutainer and the blood is put into a container called a vial. The vial is then sent to a laboratory for analysis.
Taking a sample of blood usually only takes a few minutes.
Does a blood test hurt?
You may feel a slight sharp pricking sensation as the needle goes into your skin, but it should not be painful.
If you don’t like needles, let the person who is taking the sample know so they can make things easier for you. If you feel anxious about your blood test, ask a family member or friend to go along with you. You can use a numbing cream on the area before the test. Just be sure to put it on early enough so it works in time.
It doesn’t happen often but sometimes people feel faint during a blood test. This is more likely to happen if you're dehydrated, so try to drink some water before having your blood test. Let the doctor or healthcare professional know if you often faint before the test as they may suggest you lie down while having your blood taken.
Needle phobia
Having an injection can be difficult if you have a needle phobia. If you need support to get over your fear, there are some simple ways you can make it easier.
What happens after a blood test?
Once the sample has been taken, you will be asked to apply pressure to the area for a few minutes. You can remove any dressing as soon as you feel able.
You may still get a small bruise or swelling where the needle went into your skin, but this is nothing to be concerned about and it should go down within a couple of days.
Different types of blood tests
The most common types of blood tests used to assess heart conditions are:
- Cardiac enzyme tests (including troponin tests) – help diagnose or rule out a heart attack.
- Full blood count (FBC) – measures different types of blood levels and can show, for example, if there is an infection or if you have anaemia.
- Thyroid function tests – show if you have an underactive or overactive thyroid gland. If your levels are abnormal, they can be related to some heart conditions and symptoms linked to having a slow or fast heart rate, or palpitations.
- Lipid profile - measures your cholesterol level and breakdown of good and bad fats found in your blood.
- Liver tests - give a breakdown of how well the liver is functioning. The liver is a vital organ with many functions and if it's not working well, it can have a major impact on the rest of the body.
- Clotting screen - measures how quickly your blood clots. This is important if you take blood thinning medication such as warfarin.
- BNP (B-type natriuretic peptides) tests – show the level of a hormone in your blood, which if elevated, can be a sign of heart failure.
- Blood glucose (HbA1C) test - measures your average blood sugar levels over the past three months, which can help find out if you have prediabetes or diabetes.
- U&E test – stands for urea (a protein found in the blood) and electrolytes which measures the levels of sodium, potassium and other important chemicals in your blood such as magnesium and calcium. These chemicals are important for the overall function of your heart and also help assess how your kidneys are working. Imbalances in the blood can be linked to medication that you may be taking.
Find out more about the different types of blood tests you may have and what they mean.
Heart Helpline & other support
- Speak to our cardiac nurses by phone, callback, email or online chat on Heart Helpline (Monday to Friday, 9am to 5pm).
- Contact us to talk to our customer care advisors, find your local BHF shop and for any comments, compliments and complaints you may have
- Sign up to our Heart Matters magazine for online information packed with health and lifestyle advice.
You can trust our health information
We've followed an eight-step process to make sure this content is reliable, accurate and trustworthy. Learn how we make our health information reliable and easy to understand.
Page last updated: June 2023
Next update due: June 2026
Want to find out more?
Tests for heart conditions booklet
This booklet describes the special tests that are commonly used to help diagnose heart diseases.
Some of the tests are also used to assess the current condition of people who have already been diagnosed with heart disease.
Did you find this page useful? Help us do more
