Having blood taken as a control for laboratory tests

When a laboratory carries out a blood test, they interpret the results using two crucial pieces of information:

  • was the blood suitable for the test both in sample type and quality? 
  • how do the results obtained from the patient compare to a normal person?
These two pieces of information act as the control or check.

For most tests, we can easily answer these questions by testing the samples in particular ways, and using information that has been generated from a lot of tests on a lot of people over time.

For some of the more unusual tests we are not able to do this and we need to have an identical blood sample from a healthy individual to test at the same time as that from the patient.

In many cases, we will ask a patient’s parent or a member of staff to give a blood sample to use as the 'control'.

Why am I being asked to give control blood?

We need to obtain control blood today to run some specific tests in the laboratory. We try to ask different people each time we need a sample, so that no one individual is asked on too many occasions.

If your child is having blood taken, then some of the blood we take from you will be used to help interpret tests they are having done. To minimise the number of people we need to take blood from, we may also use the blood for other tests being run in the laboratory today.

How much blood will I be asked to give?

This will vary, but it will normally be about 10ml, which is about two teaspoons.

Do I have to agree to have blood taken?

If you would prefer not to have blood taken then you should say no, and you do not have to give us a reason. This will not influence any testing or other care being provided for your child.

If you fall into one of the following categories you should definitely say no:

  • you are anaemic

  • you carry a blood borne virus, such as hepatitis B or HIV

  • you are on medications regularly

  • you have any other significant illness

Will I be identified as the person who gave the control blood?

No, we ask only that blood tubes are labelled as adult control and the date and time the blood was taken. If any further details are given on the sample, the laboratory will log these, but this information will only be available to laboratory staff and is not logged in any hospital computer systems.

Might I have the disease the laboratory is testing for?

The conditions that we are testing for are very rare, and if you are healthy, it is extremely unlikely you will be affected by them. In the unlikely event that the results were abnormal, and clear details were given on the blood tube as to the identity of the individual, appropriate counselling and further testing would be provided.

Will I be told the results of tests where my blood has been used as a control?

No, although if your blood has been used as a control for tests on your child then your clinical team will of course discuss those results with you.

Who do I ask if I would like more information?

If you would like more information, then please either ask the doctor or nurse who saw you in clinic, or ask to speak to one of the laboratory team. If you do decide to give control blood, we would like to thank you on behalf of the hospital and the patients that these tests will help us treat.

Compiled by:
The Laboratory Medicine team in collaboration with the Child and Family Information Group
Last review date:
April 2016