Red cell volume test

A red cell volume test measures the amount (volume) of red cells and plasma that your blood contains. The test helps us to diagnose true polycythemia (sometimes called erythrocytosis). A red cell volume test is the main test used to diagnose polycythaemia vera (PV).

Red cell volume tests are done in the nuclear medicine department.

Preparing for a red cell volume test

There is no special preparation for this test. You can eat, drink and take any medicines as normal. You should be prepared to be at the hospital for 2 hours 30 minutes to 3 hours.

If you are breastfeeding, contact the department before your appointment so we can give you more information before you come for your test.

If your veins are usually hard to find, and it is difficult to take blood samples, please tell us before you come for your test. If possible, please tell us as soon as you receive your appointment.

During a red cell volume test

You will meet our team of technologists, or radiographers and they will explain the procedure to you. You can ask any questions about the test.

We will take 2 blood samples. We will insert a small plastic tube (cannula) into your arm, and use this to take blood samples. After this you will be injected (in the other arm) with stannous chloride. This is a medicine that prepares the blood for mixing in the laboratory.

We will then ask you to come back 30 minutes later, and we will take another blood sample. You will then be asked to return about 1 hour later.

During this time, the red blood cells in your blood sample will be mixed with a tracer, which is a radioactive fluid. This sample will then be injected back into you. Using the cannula, we will take more blood samples at 10, 20 and 30 minutes after the injection.

During the gap between blood samples and injection you can leave the department, but you must return in time to have the later blood samples taken. Exact return times will be given to you on the day of your appointment.

Pregnancy and breastfeeding

As the test involves an injection of a radioactive tracer, you must tell us if you are, or think that you might be, pregnant, or if you are breastfeeding. If possible, please tell us as soon as you receive your appointment.

For all nuclear medicine tests we check your pregnancy status with you before using any radioactive tracer.

Pain during the test

Inserting the cannula might be painful for a moment, but this soon disappears. The injection is similar to a blood test.

After a red cell volume test

There are no side effects from this test and you can carry on with your normal activities.

After the test you will still have some radioactivity left in your body, but this is not a risk to you or other people around you.

Risks of a red cell volume test

We feel that the potential benefits of the test outweigh the very small risks. We make sure the amount of radiation you receive is as small as possible.

You can read government information about radiation exposure from medical imaging.

There are no side effects from this medicine injection.

It is perfectly safe for you to travel abroad after your test, but many airports and sea ports are now equipped with very sensitive radiation detectors. It is possible that the very small amount of radioactivity left in your body could set off a detector as you pass through security. If you plan to travel abroad in the week after your test, it could be helpful to take your appointment letter with you.

Follow-up appointments

If you already have an appointment booked in clinic to discuss the results of the test, please let our team know.

Your images will be reviewed by one of our team and a report will be sent to the doctor that referred you. You will get the test results from them.

Resource number: 5369/VER1
Last reviewed: July 2023
Next review due: July 2026


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Contact us

If you have any questions about your test in the nuclear medicine department, please contact us

Phone 020 7188 4112, Monday to Friday, 9am to 5pm

Email [email protected]

Do you have any comments or concerns about your care?

Contact our Patient Advice and Liaison Service (PALS)

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