Preparing for Your Scan
What Happens If You — Ate Before Your PET Scan?
If you have eaten or drunk something you should not have before your PET scan, the most important thing to do right now is call the centre — not panic, and not assume the scan is cancelled. The team makes that decision after hearing exactly what happened.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026
- Call first, do not just turn up — The centre needs to know before they prepare the radiotracer. Calling gives them time to advise you.
- What you ate matters more than you think — A sip of plain water is very different from a meal. The team will ask for specifics.
- Rescheduling is common and expected — This happens often. Most patients are seen again within a few days, not weeks.
- A delayed scan beats a misleading one — A poor-quality result can affect the decisions made about your treatment. Getting it right is worth the wait.
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If you ate before your PET scan, call the centre now — before you go. Whether the scan can still happen depends on what you ate, how long ago, and your blood glucose when you arrive. The team will decide; do not assume it is cancelled. Most patients are rescheduled within days.
CION does PET-CT in Hyderabad from Rs 10,499 — among the lowest published prices in the city, with no hidden charges. Indicative price, as of September 2026.
What should I do right now?
Stop eating and drinking anything further
Do not try to fast longer to compensate. Once you have eaten, the effect on your blood glucose is already under way, and continuing to fast will not reverse it quickly enough.
Call the PET scan centre before you leave home
Do not simply arrive and hope for the best. Call the number on your appointment letter, explain what happened, and wait for their instruction.
Tell them exactly what you had and when
Be specific — what you ate or drank, how much, and the time. The team cannot make a good decision without accurate information, and there is no version of this that gets better if you minimise it.
Follow whatever the centre advises
They will tell you to come in as planned, delay your arrival, or reschedule. Follow that instruction rather than guessing.
If asked to come in, eat and drink nothing more
Your blood glucose will be checked on arrival. The lower it is at that point, the better the chance the scan can still go ahead.
What should I tell the centre when I call?
- What you ate or drank, and roughly how much
- The time you ate or drank it
- Whether you have diabetes or take medication that affects blood sugar
- Whether you have already left home and how far away you are
- What the scan is for and who referred you
PET-CT Partner Centres
PET-CT Scan Centres in Hyderabad
CION offers PET-CT scans through 4 trusted partner PET-CT centres across Hyderabad, so you can choose the one closest to you. Call 18002028726 and we’ll guide you to the earliest available appointment.
PET-CT Centre — Punjagutta
PET-CT Centre — Himayatnagar
PET-CT Centre — Narayanaguda
These are partner diagnostic centres within the CION network. Toll-free booking: 18002028726.
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Will the scan go ahead, or will it be rescheduled?
| What you had | Likely outcome | What to tell the centre |
|---|---|---|
| Plain water only | Scan can usually still go ahead | Tell them anyway — they will confirm |
| Black coffee or plain tea, no sugar or milk | Often acceptable — call to confirm | Mention it specifically when you call |
| Small amount of food (a biscuit, a few nuts) | Depends on blood glucose on arrival | Call immediately — the earlier the better |
| Sugary drink, juice, or milk | Scan likely needs to be rescheduled | Glucose rises quickly with these — call now |
| Full or substantial meal | Scan will almost certainly be rescheduled | Call as soon as possible so a new slot can be found |
Why does eating before a PET scan affect the result?
A PET scan uses a radioactive glucose tracer to find areas where cells are using energy unusually fast. That is how it detects cancer activity — by following the energy. Before the tracer is injected, the centre checks your blood glucose. If the level is too high, the tracer will not go where the team needs it to go.
When you eat, your blood glucose rises. Your body releases insulin in response, and the tracer gets absorbed by normal tissues — muscles and fat — instead of concentrating in the areas being investigated.
This is not a bureaucratic rule. A scan done on a fed stomach can produce a misleading result — missing something real, or suggesting something that is not there. That is why the preparation matters, and why the team will not proceed if the conditions are not right.
Did you know?
A PET scan that has to be repeated means a second dose of the radiotracer and a second radiation exposure.
Getting the preparation right the first time is the only way to avoid that. The fasting instruction protects you, not just the image quality.
Source: International Atomic Energy Agency (IAEA) — Radiation Safety in Nuclear Medicine Programmes
CION does PET-CT in Hyderabad from Rs 10,499 — among the lowest published prices in the city — including an oncologist-reviewed report and a free Rs 950 consultation. Indicative price, as of September 2026.
Explore 92 more Preparing For and Having Your Scan Safely topics
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- Cumulative Radiation From Repeated Scans
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Your next step
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Common questions
Frequently asked questions
Will my scan definitely be cancelled if I ate something?
Not necessarily. Whether your scan goes ahead depends on what you ate, how long ago, and your blood glucose level when the centre checks it on arrival. Plain water rarely causes a problem. A full meal almost always means rescheduling. Anything in between is a judgement the nuclear medicine team makes at the time, with your specific details in front of them. Call the centre — do not assume either way before they have heard exactly what happened.
How soon can I be rescheduled?
Most centres can find an appointment within a few days to a week, though it depends on how busy the schedule is at the time. Call and explain what happened — centres expect this and have a process for it. Tell the booking team if your situation is clinically urgent, as they can sometimes prioritise accordingly. The wait is frustrating, but a scan done on the right preparation gives a result your team can actually trust.
I have diabetes — does this change what I should do?
Yes. Fasting and diabetes require a specific plan that should have been agreed between your oncologist and the nuclear medicine team before your scan day. If something went wrong with that plan, or if no plan was discussed, call both the centre and your treating team now. Do not adjust any of your diabetes medication on your own. They will advise the right next step for your specific situation.
I only had a sip of plain water. Is that a problem?
Plain water is generally not a problem for PET scan preparation. The concern is glucose in your blood, and plain water does not affect that. Still tell the centre when you call — they will confirm your scan can go ahead. If your water had any flavouring, sugar, or glucose added, mention that specifically, because those do matter and the team needs accurate information to advise you correctly.
Will this delay affect my treatment?
For most patients, a short delay of a few days does not change the treatment plan or the outcome. If you feel your situation is particularly urgent, say so when you call the centre — they can sometimes prioritise rescheduling. If you are unsure whether the delay has any clinical significance for you specifically, ask your oncologist. They are the right person to weigh your circumstances against the short wait.