Before your PET-CT scan
What Blood Sugar Level — Is Needed for a PET-CT Scan?
Your blood sugar is measured before a PET-CT scan begins. If it is above the accepted level, the scan is postponed that day — after you have already fasted, travelled, and paid. Knowing the cut-off, and why it exists, is how you protect the appointment.
Medically reviewed by Dr. C. Raghavendra Reddy, Medical Oncologist, MBBS (Gold Medal) · DNB · DM (Medical Oncology, Gold Medal) · Last reviewed September 2026
- There is a specific cut-off — Most centres will not proceed if your blood glucose is above approximately 200 mg/dL on arrival.
- High sugar ruins the image — The tracer is a glucose-like molecule. When blood sugar is high, normal cells absorb it instead, and the scan becomes unreadable.
- Diabetes patients need a plan — Medication timing on the day of the scan must be agreed with your treating doctor and the centre when you book.
- Check before you travel — A high reading at home is a sign to call the centre before making the journey.
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Most PET-CT centres will not proceed if your blood glucose is above approximately 200 mg/dL (11 mmol/L) on arrival, a threshold cited in SNMMI and EANM guidance. High glucose competes directly with the radioactive tracer, degrading the image. If your level is above the cut-off on the day, the scan is postponed.
At CION, a whole-body PET-CT starts from Rs 10,499 — among the lowest published prices in Hyderabad. Indicative price, as of September 2026.
How do you prepare your blood sugar for a PET-CT scan?
Tell the booking team you have diabetes
Do this at the time of booking, not on the day of the scan. The centre will give you specific preparation instructions based on your medications and your usual glucose control.
Fast for the period your team advises
Food raises blood glucose and activates the muscles and organs that absorb the tracer. Plain water is not just allowed — it is encouraged throughout the fasting period.
Follow your medication instructions exactly
The timing of diabetes tablets and any insulin on the morning of the scan must be confirmed with your treating doctor and the centre when you book. Do not adjust on your own.
Avoid exercise before the scan
Physical activity changes how muscles absorb the tracer and can make the scan harder to interpret. Rest on the morning of the appointment.
Check your blood glucose before you leave home
If your reading is already raised before you travel, call the centre. Arriving with a level above the cut-off means the scan cannot proceed that day and you will need to rebook.
Your glucose is measured again at the centre
This is the reading that decides whether the scan goes ahead. If it is within range, preparation is complete and the scan begins.
What should you do before leaving home for your PET-CT appointment?
- Tell the centre you have diabetes at the time of booking — not on arrival
- Fast from all food for the number of hours your team has advised
- Drink plain water freely — it is encouraged and helps the tracer clear through the kidneys
- Avoid sweet drinks, fruit juice, and glucose tablets entirely
- Follow your team's exact guidance on diabetes medication for the morning of the scan
- Do not exercise on the morning of your appointment
- Check your blood glucose before you travel and call the centre if it is already raised
- Bring your glucose meter to the appointment
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 does the centre do based on your glucose reading on arrival?
| Blood glucose on arrival | What happens next |
|---|---|
| Within the accepted range (usually below approximately 200 mg/dL / 11 mmol/L) | Scan goes ahead as planned |
| Borderline — slightly above the threshold | Team may wait briefly, retest, and decide whether to proceed |
| Clearly above the threshold | Scan is postponed to a new date — the image cannot be used clinically |
Did you know?
The tracer used in a PET-CT scan, called FDG, is a modified glucose molecule. When blood sugar is high, normal cells absorb the ordinary glucose circulating in the blood in preference to the FDG.
The tracer fails to concentrate where it should, cancer signals fade into the background, and the scan becomes clinically unreliable. The cut-off is not a formality — it is the point at which the image stops being trustworthy.
Source: SNMMI and EANM Joint Procedure Guidelines for Tumour Imaging with FDG PET/CT
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
Diabetes & Blood Sugar for PET-CT
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- The Cannula: Bruising, Pain and Difficult Veins
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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
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
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- 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
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Common questions
Frequently asked questions
What is the exact blood sugar cut-off for a PET-CT scan?
SNMMI and EANM guidance cites approximately 200 mg/dL (11 mmol/L) as the upper limit for a diagnostically reliable FDG PET-CT scan. Some centres apply a lower threshold. The cut-off your centre uses will be confirmed when you book. The reading that counts is the one taken at the centre on the day — not your reading at home — so check before you travel and call ahead if your glucose is already raised.
Why does high blood sugar actually ruin the scan?
The tracer, FDG, is a modified glucose that cancer cells and active normal cells absorb. When blood sugar is raised, ordinary glucose is already flooding those same uptake pathways. Cells take up the circulating glucose instead of the FDG, so the tracer does not concentrate where it should. Tumour tissue can appear dimmer than it really is, and inflamed normal tissue can look brighter. The result is an image your oncologist cannot rely on to make treatment decisions.
Can I eat or drink anything before a PET-CT scan?
Fast from all food for the period your team advises. Plain water is not only allowed but encouraged — it helps the tracer clear through the kidneys and improves image quality. Avoid everything sweet: juice, tea with sugar, glucose tablets, and sugar-containing gum. Your exact fasting window will be confirmed when you book, and you should follow those instructions rather than a general guide.
What should I do about my diabetes medication on the day of the scan?
Do not adjust any medication without guidance from your treating doctor and the scanning centre. The right approach depends on which medicines you take, your usual glucose control, and the time your scan is scheduled. This must be agreed in advance — ideally at the time of booking — because there is no single rule that applies to everyone on diabetes treatment. Telling the centre you have diabetes when you arrive is too late for them to help you prepare properly.
What happens if my blood sugar is too high when I arrive for the scan?
The centre measures your glucose before the scan starts. If it is above the threshold, the scan cannot go ahead that day — the image it would produce would not be clinically usable. You will be rescheduled and will need to repeat the full preparation, including fasting and travel, on a new day. Checking your glucose at home before you leave, and calling the centre if it is already raised, gives the team a chance to advise you before you make the journey.