What is a GFR test?

GFR stands for Glomerular Filtration Rate, which is a measure of how well the kidneys are working. A nuclear medicine GFR test gives an accurate measure of overall kidney function, but it cannot distinguish the contribution of each kidney separately. GFR can be measured by seeing how quickly a radioactive tracer disappears from your blood. 

Is it safe for me to have the test?

For this test it is necessary to inject a very small amount of radioactive tracer, called a radiopharmaceutical, in order to measure your GFR. The very small risk from this (similar to a chest X-ray) is outweighed by the information that will be gained by the measurement. A doctor will have checked the request to make sure this is the appropriate test for you.  

If you have any concerns or would like further information, please contact the department where you are having your GFR test. If you don’t understand why you need to have this test, please speak to the doctor who referred you. 

For female patients  aged 12 to 55 

If you know that you are pregnant, or there is any chance that you might be pregnant, please contact the department where you will be having your test. Do this as soon as possible as the scan can be postponed if it is not urgent. 

Also, contact the department if you are breast-feeding, as they may give you special instructions. 

Preparation for your test

You may eat a light breakfast or lunch but avoid high protein foods. You should also avoid large quantities of drinks containing caffeine after 10 pm on the evening before the test, but otherwise keep a normal intake of fluids. Avoid excessive exercise before and during the test.  

Please bring an up-to-date list of medications/prescription with you to your appointment.  

Your test

A small amount of radioactive tracer will be injected into a vein in your arm. You may have had a blood test in the 
past; this is much the same. The ‘pinprick’ of the needle may hurt a bit but that is all. 

Then one or more blood samples will be taken from a different vein over the next few hours. The last sample may be five hours or more after the injection. 
 
You can continue to eat during this time but continue to observe the diet and exercise restrictions mentioned in the preparation section. Maintain a normal intake of fluids. 

After your test

It is very unlikely that you will feel any side-effects after the test, but if you think that you have, please let the nuclear medicine department know.  

You may continue all your normal activities unless you have been advised otherwise.  

The radioactivity in your body will soon disappear. 

Travelling abroad

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. So it is possible that the very small amount of radioactivity left in your body could set off a detector as you pass through security. Therefore, if you intend to travel abroad within a week 
following your test, it could be helpful to take with you something to explain that you have recently had a nuclear medicine test. This could be your appointment letter or some other official confirmation from the department where you had your test.

Your results

The result of your GFR test will be looked at by a specialist who will issue a report. The report will be sent to the doctor who requested your test rather than to your GP. This is because the doctor who requested your test will have all the results from other tests and will be able to tell you how the result of your GFR test affects your care. 

Information about you

As part of your care, information will be shared between clinical staff, some of whom you may not meet. It may also be used to help train other staff. Information collected may also be used later on to help the department improve their quality of care, plan services or to research into new developments. 

The results of your test may be used to teach other healthcare workers, but your name and all other identification will be removed first. It won’t be possible to identify you from the results. 

All information will be treated as confidential and is not given to anyone who does not need it. If you have any concerns, please discuss these with the department.

More information

All the staff would like to make your visit as pleasant as possible. If you have any concerns, please talk to a member of the nuclear medicine staff.

A printable version of this leaflet can be found here