Preparing for your scan
Fasting Before a PET-CT Scan: — How Long and Why
You need to fast from food and all drinks except water for at least six hours before a PET-CT scan. If you arrive having eaten, the scan will usually be postponed. Knowing why the fast matters makes it easier to get right.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed September 2026
- Six hours, water only — Food raises your blood glucose and competes with the tracer. Plain water does not.
- Even a small amount counts — A single snack within six hours can be enough to make the images unreadable.
- Diabetes changes the preparation — If you have diabetes, speak to your treating team before the scan — the preparation is different for you.
- Tell them if you have eaten — Say so immediately when you arrive. Staff will check your blood glucose and decide whether to proceed.
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Fast for at least six hours before your PET-CT scan. Plain water is allowed and encouraged throughout. Food raises your blood glucose, which competes with the radioactive tracer — the scan then cannot reliably show where cancer is. If you have diabetes or kidney problems, your treating team will give you separate instructions before the day.
A whole-body PET-CT at CION costs from Rs 10,499 — among the lowest published prices in Hyderabad. Indicative price, as of September 2026.
Why does food ruin a PET-CT scan?
The tracer used in a PET-CT scan is a glucose-like molecule. Your body cannot tell it apart from ordinary glucose, so it is absorbed by whichever tissue is using glucose most actively — and cancer cells tend to use far more than normal cells do. That difference is what the scanner reads to find where cancer is.
When you eat, your blood glucose rises. That extra glucose floods the same absorption pathways the tracer needs. The tracer gets diluted and taken up by muscle and normal tissue rather than concentrating where cancer is. The resulting images are unreliable.
A scan done on a patient who has eaten cannot be interpreted accurately and will usually be postponed. The fast protects the hours you have already spent getting to this point.
What can you eat or drink before a PET-CT scan?
- Fast from all food for at least six hours before your appointment time
- Plain water only — drink freely right up to your appointment and arrive well hydrated
- No tea, coffee, juice, milk, alcohol or fizzy drinks — including diet and sugar-free versions
- No chewing gum, mints or sweets
- Avoid strenuous exercise in the 24 hours before the scan — active muscles absorb the tracer and interfere with the results
- If you have diabetes, tell the scanning centre when you book, not on the morning of the scan
- Ask your treating team or the scanning centre about your regular medicines before scan day — do not change or stop them on your own
- Wear loose, comfortable clothing with no metal zips or underwire — you may be asked to change
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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What happens on the day of your PET-CT scan?
Arrive and check in
Arrive at the imaging centre at your booked time and confirm your preparation with staff. Tell them immediately if you have eaten or had anything other than water.
Blood glucose check
A staff member checks your blood glucose before giving the tracer. If the reading is outside the acceptable range for a reliable scan, your appointment will be rescheduled.
Tracer injection
A small amount of radioactive tracer is injected into a vein, usually in your arm. The injection itself takes only a moment.
Rest period
You rest quietly for around an hour while the tracer travels through your body and is absorbed by active tissue. Staff will ask you to stay still and calm — physical and mental rest during this time helps the tracer concentrate where it needs to.
The scan
You lie still on the scanner table while the machine takes images. The scanner is open on both sides. Staying still is important — movement blurs the images.
After the scan
You can eat and drink normally as soon as the scan is complete. Staff will tell you about any precautions for the rest of the day before you leave.
Did you know?
Cancer cells absorb glucose at a far higher rate than most normal cells — a difference the FDG tracer in a PET-CT scan is specifically designed to detect.
When blood glucose is elevated from eating, both normal and cancer cells compete for the tracer. The signal that makes cancer visible gets weaker, and the scan can no longer do what it is designed to do.
Source: EANM/SNMMI Guideline for 18F-FDG use in Oncology
Book a PET-CT at CION from Rs 10,499 — among the lowest published prices in Hyderabad — with an oncologist-reviewed report and a free Rs 950 consultation, across 4 partner centres. Indicative price, as of September 2026.
Explore 92 more Preparing For and Having Your Scan Safely topics
Preparing for Your Scan
- A Printable PET-CT Preparation Card
- Can I Drink Water Before a PET-CT Scan?
- Can I Have a PET-CT Scan During My Period?
- Can I Take My Regular Medicines Before a PET-CT Scan?
- Can You Reschedule a PET-CT Scan?
- Cold Weather, Shivering and Brown Fat: Why You Are Asked to Stay Warm
- Fasting Before a PET-CT Scan: How Long and Why
- How to Prepare for a PET-CT Scan: The Complete Checklist
- Preparing a Very Elderly or Frail Person for a PET-CT
- Preparing a Wheelchair-Bound or Bedridden Patient
- Preparing for a PSMA, DOTATATE or FAPI PET-CT
- Should I Avoid Exercise Before a PET-CT Scan?
- Smoking, Alcohol and Caffeine Before a PET-CT Scan
- What Happens If You Break the Fast by Mistake?
- What to Carry to Your PET-CT Appointment
- What to Eat the Day Before a PET-CT Scan
- What to Wear to a PET-CT Scan
- Why Your Kidney Function Test Is Needed Before a PET-CT
Contrast, Cannula & Procedure Safety
- Can You Have a PET-CT If You Are on Blood Thinners?
- Can You Have a PET-CT Through a Port or PICC Line?
- Contrast Allergy and PET-CT: What to Declare
- Contrast Reaction Symptoms: What to Watch For
- Contrast and Kidney Function: The Creatinine Rule
- Infection Risk and Hygiene at a Scan Centre
- Is Contrast Used in a PET-CT Scan?
- Metformin and Contrast: What Is the Rule?
- Side Effects of a PET-CT Scan
- The Cannula: Bruising, Pain and Difficult Veins
- Tracer Leakage at the Injection Site (Extravasation)
- What If You Feel Unwell During the Scan?
Diabetes & Blood Sugar for PET-CT
- A Diabetic Patient's PET-CT Day Plan
- Best Appointment Time for a Diabetic PET Scan
- Can Diabetics Take Their Tablets Before a PET Scan?
- Does Diabetes Change Your SUV Reading?
- Fasting Safely With Diabetes Before a Scan
- Insulin and PET-CT: Timing Rules
- Newly Diagnosed Diabetes Found Before a Scan
- PET-CT Scan With Diabetes: The Complete Preparation Guide
- PET-CT With Steroid-Induced High Sugars
- What Blood Sugar Level Is Needed for a PET-CT Scan?
- What Happens If Your Sugar Is High on the Day?
- What to Eat the Day Before if You Have Diabetes
Radiation Safety & After-Scan Precautions
- Are You Radioactive After a PET-CT Scan?
- Being Around Pregnant Women After a PET-CT Scan
- Can I Hold My Child or Grandchild After a PET-CT Scan?
- Can a PET-CT Scan Cause Cancer?
- Cumulative Radiation From Repeated Scans
- Do You Need Precautions After a PSMA or DOTATATE Scan?
- Do You Need Separate Utensils or a Separate Toilet After a PET-CT?
- How Long Does the Tracer Stay in Your Body?
- How Long Should You Avoid Close Contact After a PET-CT?
- How Many PET-CT Scans Are Safe in a Year?
- How Much Radiation Is in a PET-CT Scan?
- Is PET-CT Radiation Different From Radiotherapy?
- Is the Radiation From a PET-CT Scan Dangerous?
- PET-CT Radiation Compared With CT, X-Ray and Natural Background
- Radiation Safety at Home After Your Scan: A Family Checklist
- Radiation Safety for Staff and Attendants at the Centre
- Simple Steps to Clear the Tracer Faster
- Travelling Home After a PET-CT Scan: Public Transport and Airports
Scan Day: What Actually Happens
- Can Someone Stay With Me During the Scan?
- Can You Drive Yourself Home After a PET-CT Scan?
- Can You Have Sedation for a PET-CT Scan?
- Can a PET-CT Scan Be Done on the Same Day as Other Tests?
- Contrast in a PET-CT Scan: When It Is Used and Why
- Eating and Drinking After Your PET-CT Scan
- How Long Does a PET-CT Scan Take?
- Is a PET-CT Scan Painful?
- Is a PET-CT Scanner Closed Like an MRI? Claustrophobia Explained
- The Tracer Injection: Does It Hurt?
- What Happens If the Scan Cannot Be Completed?
- What If You Cannot Lie Still or Have Tremors?
- What to Expect Immediately After the Scan
- Why Was My Scan Repeated or Extended on the Day?
- Why You Have to Wait an Hour After the Injection
- Your PET-CT Scan Day: What Happens, Step by Step
Special Populations
- Breastfeeding and PET-CT: How Long to Pause
- PET-CT Scans for Children: A Parent's Guide
- PET-CT With Kidney Disease or on Dialysis
- PET-CT With a Pacemaker, Stent or Metal Implant
- PET-CT for Claustrophobic Patients
- PET-CT for Patients Who Cannot Lie Flat
- PET-CT for Patients With Anxiety or Panic Disorder
- PET-CT for Patients With Dementia or Confusion
- PET-CT for Patients With Incontinence or a Catheter
- PET-CT for Patients With a Stoma
- PET-CT for Patients on Long-Term Steroids
- PET-CT for Very Elderly or Frail Patients
- PET-CT for Very Heavy Patients: Weight and Bore Limits
- PET-CT for Wheelchair and Bedbound Patients
- PET-CT in Pregnancy: Why It Is Avoided
- Sedation and Fasting for a Child's PET Scan
Your next step
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Common questions
Frequently asked questions
Can I take my regular medicines before the scan?
Do not change or stop your regular medicines on your own. Contact the scanning centre or your treating team before scan day and ask them directly — they will tell you which medicines to take as usual and whether any need to be timed differently. This is one of the things they confirm when you book, so raise it then if you have not already.
What if I accidentally ate something before my scan?
Tell the scanning centre as soon as you arrive — or call ahead if you realise before leaving home. They will check your blood glucose on arrival and decide whether the scan can still go ahead or needs to be rescheduled. Saying nothing and hoping for the best risks a wasted journey and images that cannot be read. Staff will not judge you for eating accidentally; they just need to know so they can make the right call.
I have diabetes — do I prepare the same way?
No. Fasting and blood glucose management on scan day is more complicated if you have diabetes, and the preparation is different. Speak to your treating oncologist or diabetologist before your scan is booked — not on the morning of — so they can give you specific guidance. Tell the scanning centre at the time of booking as well, so they are prepared for your arrival.
Can I drink tea or coffee as long as there is no sugar in it?
No. Tea and coffee are not allowed, even without sugar or milk. Caffeine causes changes in blood flow that affect how the tracer is distributed through the body, independently of glucose. Fizzy drinks, juice, coconut water and flavoured water are also not allowed. Plain still water is the only drink permitted in the hours before the scan.
How long will the whole appointment take?
Allow most of a morning or afternoon. After you arrive, there is a blood glucose check, the tracer injection, a rest period of around an hour, and then the scan itself. You will not be in the scanner the whole time, but the total time from arriving to leaving is usually longer than people expect. Ask the scanning centre for the expected duration when you confirm your booking, so you can arrange transport or any carer support well in advance.