# FDG PET-CT scan preparation: fasting, blood glucose and diabetes

Source: https://onco.cc/protocols/fdg-pet-ct-preparation/  
OnCo record `fdg-pet-ct-preparation` (Protocol). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A PET-CT scan uses a sugar-like tracer, so food, sugar, exercise and cold can all blur the pictures. Do not eat for at least 4 hours before (plain water is fine and helps), take your usual medicines, avoid hard exercise the day before, and keep warm. If you have diabetes, the unit will give you a plan for your tablets or insulin and will check your blood sugar when you arrive.

## Summary

EANM 2015 (version 2.0, ungraded): nothing but plain water for at least 4 hours before the FDG injection; medication as prescribed; about 1 litre of water in the 2 hours before; no coffee, caffeinated or 'sugar-free' drinks; glucose-containing intravenous fluids and parenteral nutrition stopped at least 4 hours before; no strenuous exercise for at least 6 hours and preferably 24; warmth from 30 to 60 minutes before injection to limit brown fat uptake; seated or lying and silent during the uptake phase, especially in head and neck cancer; void before imaging. Blood glucose must be measured before FDG; in clinical studies scanning proceeds below 11 mmol/L (about 200 mg/dL) and is rescheduled at or above it, though hyperglycaemia in brittle diabetes is not an absolute contraindication. Insulin to lower glucose is given only if more than 4 hours will pass before FDG (rapid-acting, subcutaneous). Type 2 diabetes on tablets: late morning slot, tablets continued; insulin-treated diabetes: late morning after normal breakfast and insulin with FDG no sooner than 4 hours after rapid-acting insulin, or early morning; insulin pumps off for at least 4 hours. Uptake time 60 minutes (55 to 75), kept within 10 minutes on repeat scans for response assessment. Pregnancy needs a clinical decision; breastfeeding need not stop, with close contact limited for 12 hours. An Australian joint diabetes and nuclear medicine guideline (2026) gives diabetes-specific protocols; it was read as a summary abstract only.

## Fields

- Kind: Protocol
- Last checked: 2026-11-11
- Also known as: PET scan preparation; PET-CT prep; fasting before PET scan; blood sugar before PET; diabetes and PET scan; FDG PET fasting; insulin before PET scan

## Connected records

- technologies: [FDG PET](https://onco.cc/technologies/fdg-pet/), [PET/CT](https://onco.cc/technologies/pet-ct/)
- ideas: [A written plan for SGLT2 inhibitors and GLP-1 medicines before an FDG PET-CT scan](https://onco.cc/ideas/idea-pu-sglt2-glp1-plan-before-pet/)

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