Blood contains fluid that is called plasma and cells. There are three kinds of cells: red, white and platelets. Blood is the body’s main carrier of oxygen, nutrients, and waste products. Blood tests give a representation of what is going on internally in your body. A blood test is the removal of blood from a vein or artery. It is usually removed from the arm of a patient near the elbow. The reason why the elbow area is used is because it does not have many nerves. Other sites that can be used are the wrist, hand and foot.

What happens during a blood test?

Initially a cord (tourniquet) is tied around the upper arm of the person to make the vein prominent. The tightness of the cord makes it much easier to remove the blood. The arm is cleaned and then a needle is inserted through the skin into the vein. The necessary amount of blood is extracted into a special tube or tubes, the needle is removed and a little ball of cotton wool is held over the wound. This should be pressed for one to two minutes before applying a band aid. The tubes are sent to a laboratory where the blood is analysed.

If only a few drops of blood are needed (for example monitoring blood sugar in diabetes) a finger-stick can be performed. A small prick is made in the tip of the finger and the blood is squeezed out. Complete blood counts can be obtained through this procedure. Blood can also be obtained from the earlobe, or from the heel of a baby.

The person performing a blood test is called a phlebotomist. Phlebotomists work in hospitals and in pathology centres such as Sullivan and Nicolaides (S&N) and Queensland Medical Laboratories (QML).

Why do you need to have a blood test?

There are many reasons why your doctor might order a blood test. Blood tests are completed to:

  • help make a medical diagnosis
  • monitor or establish treatment
  • screen for undiagnosed medical conditions
  • grow the infectious organisms that cause an illness to see exactly what they are through a microscope.

What do I need to do after the blood test?

After the blood test you do not need to do anything in particular. Most people do not have any side effects from having a blood test. There could however be some swelling, bruising, or pain. First-aid procedures could be used to relieve the pain, such as putting ice on the site or general pain relief could be given. It could also help to not use the affected arm as much as possible.

Understanding Your Blood Tests

It is important to be informed about your medical care. When a test is ordered for you, it is good to know why the test is ordered, how it will be done, and what the doctor expects to learn from it. Here are some good questions to ask:

  • Why does this test need to be done? How could it change the course of my care?
  • What do you (the patient or caregiver) need to know or do before the test?
  • What happens during and after the test?
  • How much will the test hurt or be an inconvenience? What are its risks?
  • How long will the test take? When will results be available?
  • Where do you need to go to take the test? Is there a "good" time to schedule the test?
  • What are normal results for my test? What do abnormal results mean?
  • What factors may affect the results?
  • What course of action may be next, after the test?