Diabetes
Preparing for your PET-CT (FDG) scan
Your healthcare provider has ordered a positron emission tomography (PET/CT) scan. This imaging test helps to find or monitor a health condition.
For this test, you’ll get an injection of a tracer. The tracer is a modified glucose (sugar) molecule called 18-fluoro-deoxyglucose (FDG). The test shows how the FDG moves through your body and which tissues take it up.
To get clear results, your blood glucose and insulin levels need to be stable before the test. It’s important to take your diabetes medicines at the right times before your test.
Your blood glucose level must be:
- below 11.0 mmol/L for a PET-CT body scan
- below 8.9 mmol/L for a PET-CT brain scan
These general instructions will help you manage your blood glucose safely for the test. If you have questions, talk with your diabetes healthcare provider before the test.
Appointment time
Your test will be scheduled for the morning whenever possible.
Eating and drinking
Do not eat or drink anything for at least 6 hours before your arrival time.
What to bring
Bring these items to your appointment:
- glucose meter or continuous glucose monitor (CGM) and sensor
- If you use a CGM, plan to change your sensor on the day of the test because you will need to remove it for the scan.
- insulin pump (if you use one) and extra supplies:
- full replacement insertion set or pod
- insulin
- new CGM sensor (if you use one)
The day before your test
Take all your diabetes medicines as usual (pills, injections, and insulin).
The day of your test
Medicines
Do not take:
- repaglinide (Gluconorm)
- gliclazide (Diamicron, Diamicron MR)
- glyburide (Diabeta)
Take all your other diabetes medicines as prescribed.
Bolus insulin
Admelog, Apidra, Fiasp, Humalog, Humulin R, Kiristi, NovoRapid, Novolin Toronto, Trurapi:
- Do not take mealtime bolus insulin for at least 6 hours before your test.
- Do not take correction bolus insulin for at least 4 hours before your test.
Basal insulin
Awiqli, Basaglar, Lantus, Levemir, Semglee, Toujeo, Tresiba:
- Take your usual morning dose of long-acting insulin.
Humulin N, Novolin NPH:
- Take 20% less than your usual morning dose.
Premixed insulin
Humulin 30/70, Humalog 25/75, Humalog Mix 50, Novolin 30/70, Novolin 40/60, Novolin 50/50:
- Do not take your morning dose.
CGM
If you use a CGM, you will need to remove your CGM sensor before the test. Follow your healthcare provider’s advice and see:
Low blood glucose before the test
Treat low blood glucose with only 15 to 16 grams of fast-acting sugar (like dextrose tablets or fast-acting glucose tablets). If you use an automated insulin pump, you may need less.
Check your blood glucose again in 15 minutes. Repeat the treatment (if needed) until your blood glucose is above 4 mmol/L.
Do not overtreat low blood glucose with more dextrose or glucose than recommended. Your test could be delayed or rescheduled.
After your test
You can restart your diabetes medicines as usual with your first meal after the test.
If you use premixed insulin, take 20% less than your usual dose with your first meal after the test, or follow your healthcare provider’s advice.
Take all other insulin as usual.
If you use a CGM, insert a new sensor.
If you use an insulin pump
Before your test:
- Keep your usual basal rates.
- Do not give any bolus doses for at least 4 hours before your arrival time.
Right before you go through the CT scanner:
- remove your insulin pump or pod
- remove your full insertion set if you use a metal cannula
- remove your CGM sensor
After your test:
- Reconnect your pump.
- Insert a new CGM sensor.
For more information, go to ipumpit.ca.
To see this information online and learn more, visit MyHealth.Alberta.ca/health/aftercareinformation/pages/conditions.aspx?hwid=custom.ab_di_fdg_pet_ct_diab_prep_inst.
For 24/7 nurse advice and general health information call Health Link at 811.
Current as of: August 12, 2026
Co-Author: Diagnostic Imaging, Alberta Health Services
Co-Author: Medicine-Diabetes, Acute Care Alberta
This material is not a substitute for the advice of a qualified health professional. This material is intended for general information only and is provided on an "as is", "where is" basis. Although reasonable efforts were made to confirm the accuracy of the information, Alberta Health Services does not make any representation or warranty, express, implied or statutory, as to the accuracy, reliability, completeness, applicability or fitness for a particular purpose of such information. Alberta Health Services expressly disclaims all liability for the use of these materials, and for any claims, actions, demands or suits arising from such use.
