Blood sugar and PET-CT
Does Diabetes Change — Your SUV Reading?
If your blood glucose is high when the FDG tracer is injected, it competes with the tracer for uptake, and the numbers in your report will be lower than they should be. Preparation exists to prevent this — and there is a specific sequence to follow.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026
- Glucose and FDG compete — High blood sugar at injection time means less tracer reaches the tumour, lowering the SUV.
- Your report notes your glucose — The nuclear medicine team records your blood glucose at injection and factors it into their interpretation.
- Preparation makes it reliable — Following the fasting and medication instructions your centre gives you is the main protection against a misleading result.
- Tell them at booking, not on the day — The centre needs to know you have diabetes before your appointment so they can give you the right instructions.
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Yes. High blood glucose competes with the FDG tracer that PET-CT uses. Both your tumour's uptake and the background uptake are affected, making SUV values lower than they would be in a person without diabetes. Guidelines from EANM and SNMMI recommend controlling blood sugar before your scan so the results can be read reliably.
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What happens at the scan centre if you have diabetes?
Tell the centre at booking
Inform the centre that you have diabetes when you make the appointment. Do not leave it until the day you arrive. The centre will give you preparation instructions based on this information.
Confirm your medication timing with your doctor
Do not adjust your diabetes medication without asking. Your treating doctor and the centre will both need to tell you what to do in the hours before the scan. Confirm this before your appointment, not on the morning.
Arrive having followed the fasting instructions
Fasting is required before PET-CT for everyone. The centre will tell you how long to fast and what you may or may not drink. Follow those instructions exactly.
Your blood glucose is checked on arrival
Before the tracer is injected, a technologist measures your blood glucose. This reading is recorded and included in your report.
If your glucose is in range, the scan proceeds
The tracer is injected and you wait in a quiet room while it distributes through your body. The scan then follows.
If your glucose is too high, the scan is rescheduled
A reading above the acceptable level means the scan cannot go ahead that day. You will be rebooked. This protects you from a misleading result — it is not a punishment for poor preparation.
What do you need to confirm before your scan day?
- Tell the centre about your diabetes at the time of booking, not on the day.
- Ask what fasting instructions apply to you specifically.
- Confirm your medication timing with both your treating doctor and the centre — do not change anything without asking.
- Bring your glucose monitoring kit so you can check at home before leaving.
- Bring a written list of your current diabetes medications and doses to give the technologist.
- Know what to do if you feel unwell during the fasting period — agree this with your doctor in advance.
- Ask whether you should bring food for after the scan.
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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Why does high blood sugar make your SUV lower?
PET-CT uses a tracer called FDG, which is a form of glucose with a radioactive tag attached. Cancer cells take it up at high rates because they consume glucose faster than normal tissue — and that difference in uptake is what the scan measures as the SUV.
When your blood is already carrying a lot of ordinary glucose, that glucose and the FDG tracer are in competition. Normal cells and tumour cells reach for whichever molecule is available. With more ordinary glucose in circulation, proportionally less FDG reaches the tumour, and the measured SUV comes out lower than it truly is.
The background tissues — muscle, liver — behave the same way. They also take up more ordinary glucose and less FDG, which reduces the contrast between the tumour and its surroundings. Lower contrast makes it harder to detect smaller or less active areas of disease.
Nuclear medicine physicians are trained to account for this. Your blood glucose at injection is recorded in the report, and the radiologist uses it when interpreting your numbers. If your glucose was elevated, your oncologist can factor that into how they read the findings — which is one more reason to share the information rather than guessing.
Did you know?
Even a moderate elevation in blood glucose at the time of FDG injection can meaningfully reduce tracer uptake in the tumour — which is why the glucose check on arrival is a clinical decision point, not a formality.
EANM and SNMMI guidelines specify that centres should reschedule rather than scan when glucose is above the acceptable level, because the alternative is a result that may underestimate disease activity.
Source: EANM/SNMMI Practice Guidelines for FDG PET-CT Imaging
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
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
Contrast, Cannula & Procedure Safety
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- 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
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- Metformin and Contrast: What Is the Rule?
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- The Cannula: Bruising, Pain and Difficult Veins
- Tracer Leakage at the Injection Site (Extravasation)
- What If You Feel Unwell During the Scan?
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
- 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
Will the centre send me home if my blood sugar is too high on the day?
Yes. If your glucose reading on arrival is above the level the centre requires, the scan will be rescheduled rather than going ahead. A scan done with high glucose produces SUV values that may underestimate how active the disease is, and your team needs an accurate result to make good decisions. If your glucose has been difficult to control recently, tell the centre before your appointment so they can plan with you in advance rather than on the day.
Can I eat normally if I am worried about fasting with diabetes?
Fasting is required before PET-CT because food raises blood glucose and interferes with the tracer. How you manage your diabetes safely during that fast is a conversation to have with your treating doctor before the appointment, not on the morning. Your doctor and the centre together will give you instructions suited to your situation. Going to the scan without that plan in place is the main reason people are sent home after travelling.
My SUV was lower in my latest scan than the one before — could blood sugar explain it?
It is one possible factor. Your nuclear medicine report records the blood glucose at injection for each scan, so if your glucose was higher on one occasion than another, that difference will be visible in the reports. Your oncologist can compare those readings alongside the SUV values to tell you whether the change is likely disease-related or preparation-related. Ask them to walk you through both numbers rather than interpreting the change on your own.
What should I do if I feel unwell during the fasting period before my scan?
Tell the centre as soon as possible. Do not simply miss the appointment without calling — they may be able to help or reschedule you without losing your slot. If you are concerned about fasting safely, raise it with your treating doctor before the fast is due to begin. Managing a pre-scan fast with diabetes is something to plan ahead, not improvise on the morning of the appointment.
Is PET-CT still the right test for me if my diabetes is poorly controlled?
Yes. PET-CT remains one of the most precise tools for staging cancer and monitoring treatment response, and having poorly controlled diabetes does not change that value. What it does mean is that your team needs to know your glucose situation before the appointment is made, so the centre can plan the right preparation approach for you. Tell your oncologist before booking rather than after, so there is time to prepare properly.