What are the risks of blood tests?

Thousands of blood tests are carried out every day in the UK; on the whole, this is a very safe procedure, however, as with all medical procedures, there are risks.

What are the risks?

It is very rare for a blood test to result in serious complications; however, there is a very small possibility of complications arising.


Infection control is extremely important and doctors and nurses taking blood are required to follow strict regulations regarding the disposal and storage of needles and blood samples; they are also required to follow procedures for labelling blood so that samples do not get lost or confused with other people’s samples. If you have your blood taken in a private or NHS hospital or surgery setting in the UK, the risk of infection should be extremely low, as staff are highly trained and regulations have been put in place to prevent the spread of infectious diseases.

In some rare cases, the site where the needle was passed into the vein may become infected; if this is the case, the wound may become red and swollen; if you notice these symptoms you should arrange to see your GP.

Excessive bleeding

It is common for the site of the test to bleed after the blood sample has been taken; however, this should stop fairly quickly after a cotton wool pad or gauze patch has been placed on the wound. In some rare cases, the wound may bleed excessively; if this is the case, your doctor or nurse will try to stem the blood flow as quickly as possible.


Mild bruising around the area where the needle went into the vein is fairly common after a blood test; however, in some rare cases, more severe bruising may develop. Severe bruising is usually caused by a lack of pressure being applied to the site of the wound after the needle has been removed (applying a cotton wool pad to the wound helps to stem the bleeding, which will reduce the risk of bruising) but it may also be caused by damage to the vein when the needle was inserted.

Fainting and dizziness

Some people may experience dizziness during or after a blood test; this is very common in people who have a fear of needles and injections. If you are feeling faint before or during a blood test, tell your doctor or nurse. Usually, dizziness will pass after you have had a minute to sit down with your head between your legs (this will stimulate blood flow to the brain).


A haematoma is a collection of blood under the skin; it is similar to bruising and is caused by the blood clotting to form a solid lump. It is fairly common to have a haematoma; if you are in pain, you should consult your GP but the bruising should heal independently over the course of time; applying ice packs may also help to ease swelling (if you do use an ice pack, make sure you wrap the ice packs up in a towel or cloth to prevent damaging the skin).

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