Do you need an empty stomach for a PET scan?

FDG is related to glucose, so food and drinks containing calories can change blood glucose and how the tracer moves through the body. Muscle activity can also affect the images. For that reason, the centre may ask you to avoid food for a set period, drink plain water, and avoid strenuous exercise. Requirements can differ according to the tracer, scan purpose, diabetes, and other medical factors.

Fasting does not mean that everyone should stop all medicines. People with diabetes may need an individual plan because missed meals or altered medication can cause unsafe glucose changes. A PET-CT uses the tracer to show activity and CT to show anatomy; preparation supports image quality but does not make a scan diagnostic by itself.

Read the appointment instructions carefully and ask what counts as a permitted drink. Tell the department about diabetes, medicines, pregnancy, breastfeeding, recent illness, or a previous difficulty fasting. Do not change insulin or other prescribed treatment without the team's direction. Arrive on time, keep warm and relaxed, and avoid vigorous activity if instructed. If you accidentally eat, drink a calorie-containing beverage, or take a medicine with food, call the imaging centre before travelling; they can decide whether the appointment should proceed.

Get advice before the scan if fasting makes you shaky, confused, sweaty, faint, or unwell, particularly if you have diabetes. Seek urgent help for severe confusion, loss of consciousness, breathing trouble, or a serious allergic-type reaction. Tell the imaging team immediately about symptoms rather than trying to continue preparation alone.

How long should I avoid food, and may I drink plain water? Which medicines should I take? What is the plan if I have diabetes or develop low glucose symptoms? Should I avoid exercise before arriving, and who should I call if I break the fast?