What is a blood test?

Blood tests are one of the most common types of medical test. They have many uses, including assessing your general health, checking if you have an infection, seeing how well specific organs are functioning and screening for certain genetic conditions.

How is the blood sample taken?

A band may be put around your upper arm to make the veins below expand and make it easier to draw blood from them. Your arm may feel tight for the short time the band is applied. The injection site will be cleaned with an alcohol swab.

You may feel a brief sting or pricking as the needle is inserted. A tube will be attached to the needle for collection. Your tests may require more than one vial of blood to be collected while the needle and tube is in place.

If you feel squeamish or nervous, it is often better not to watch. If you find yourself feeling faint or light-headed before, during or after the procedure, tell the nurse or phlebotomist. There should be the option for you to lie down. Similarly, if you have had this sort of reaction in the past, tell the nurse or phlebotomist in advance.

Inform nurse or sample taker of any concerns

Some people feel nervous about having blood taken; however, the person taking the sample (your practice nurse or, at a laboratory, a person called a phlebotomist) is trained in this procedure, and it is usually straightforward.

If you have previously experienced problems having blood taken, inform the nurse or phlebotomist beforehand of any concerns you have, so they can attempt to minimise these.

What happens afterwards?

After the blood sample is taken, a cotton swab is applied to the site and held there for at least 3 minutes with a firm pressure. This will stop bleeding and help minimise any bruising. A plaster is applied, which can be removed after about half an hour.

Once leaving the practice/laboratory, you should avoid strenuous activity or heavy lifting with the arm for about one hour.

Some people develop a bruise at the injection site – some people bruise more easily than others. Any small bruise should fade after a few days.

Less common reactions to a blood test

Less often, there may be bleeding after the sampling, or a lump (called a haematoma) may develop at the injection site. If so, firm pressure should be applied for 10-15 minutes. A cold pack (eg, ice cubes in a plastic bag or wrapped in a cloth) can also reduce swelling.

The injection site may be tender and a more extensive bruise may develop from a haematoma. The bruise can take up to 10 days to go away, but there are no long-term side effects from this. If you have any ongoing concerns after the procedure, contact your doctor or laboratory nurse.

Learn more

Common laboratory tests – a patient's guide Family Doctor NZ