How Much Blood Is Taken During A Blood Test?

There are countless reasons why a blood test may be needed, and we provide a specialised, personalised service to ensure that you can not only be provided with standard tests but can request custom tests for certain situations and conditions.

There are hundreds of different blood tests available in part because the blood contains a lot of different cells, antibodies and biological markers that can be measured through a battery of processes to test anything from general health to natural immunity to a disease.

Whilst some blood tests are done using spot cards, particularly when screening newborn babies for rare diseases, many involve drawing blood from the inside of the elbow or the wrist.

One of the most common questions that a healthcare professional undertaking a blood test will receive is how much blood will be taken during a blood test.

Whilst the answer can vary slightly depending on the tests that need to be done, the important point is that it is enough to undertake any necessary tests but not so much that it will cause any significant side effects.

How Much Blood Is Taken Per Test?

It is difficult to say exactly how much blood will be taken during a blood test, as it can vary depending on how many tests are being done at the same time and thus how many samples need to be collected.

For example, a general full blood count (FBC) test needs just 1 ml of blood to do, but this is often undertaken with a common inflammation test known as the erythrocyte sedimentation rate (ESR), which would require 2.5 ml to do.

Chemical tests usually require 2.5 ml as well, and other types of tests can require up to 10 ml of blood, so if you have a range of tests at the same time, you may have up to 30 ml of blood taken out, or slightly more than a shot glass.

It is typically unusual to take that much, however, as most samples can be used for multiple tests, not all of them need to be filled entirely and if a lot of tests need to be done, they will often be arranged to take place over multiple appointments.

Are There Any Side Effects Of Having Blood Tests?

Unlike donating blood, where up to 470 ml of blood is taken, even a collection of tests is unlikely to have any side effects outside of slight bruising, swelling or sensitivity around the place where blood was taken.

The blood production system in your bone marrow is very efficient at producing new blood cells, and much of the volume of blood that is taken for testing purposes will be quickly replenished.

However, if you do feel dizzy, faint or lightheaded, let the healthcare professional who took the test know immediately.

As well as this, let them know before the test if you are uncomfortable with needles, as they will do their utmost to help you feel relaxed and comfortable whilst drawing blood.