PET CT is generally very safe. Learn the possible side effects of the injection and the scan, how to reduce them and when to call your doctor.
PET CT scans rarely cause side effects. Most people feel nothing, and a few notice mild pain at the injection site, a metallic taste or anxiety. Serious allergic reactions to the tracer are extremely rare, but if CT contrast is also used, mild contrast reactions can occur.
Side Effects of the Tracer
FDG is a tiny amount of sugar-like material, so allergic reactions are extremely rare. Some people feel a cool sensation in the arm or see a bruise from the needle. These settle quickly. Radiation exposure itself does not cause immediate symptoms. See FDG tracer explained.
Possible effectHow commonWhat to doPain or bruise at injection siteOccasionalCold compressMetallic taste or warmthOccasional with contrastPasses in a minuteAnxiety or claustrophobiaSome peopleTell the staffRash or itchingRareReport to staff or doctorSerious allergyVery rareEmergency treatment is availableSide Effects of CT Contrast
If contrast is used in the CT part, you may feel warmth, a metallic taste or a feeling of needing to pass urine. Rarely, itching, rash, nausea or vomiting occurs. People with kidney disease need extra checks. Read CT scan side effects and contrast reactions.
Effects of Fasting and Lying Still
- Hunger, headache or dizziness after fasting, especially in diabetic patients. Carry a snack to eat right after the scan.
- Back or neck stiffness from lying still, which settles quickly.
- Feeling cold in the scan room; ask for a blanket.
Long-Term Effects
A single PET CT carries a very small increase in lifetime cancer risk, as with other radiation-based scans. Doctors weigh this against the benefit of finding or staging disease. See PET CT radiation and safety.
Precautions and When to Call Your Doctor
- Drink water and empty your bladder often.
- Keep a distance from pregnant women and infants for some hours if advised.
- Call your doctor if you have a rash, swelling, breathing trouble, fever, or a painful, swollen arm at the injection site.
A Practical Example
Tariq, 59, felt dizzy at the end of a long fast before his PET CT because he has diabetes. The staff checked his sugar, gave him juice after the scan and advised him to bring a snack next time. He had no other effects. Planning for fasting problems removed the main discomfort of the test.
After the Scan and Key Facts
- Side effects are rare and mostly mild
- Plan for fasting, especially in diabetes
- Tell staff about allergy and anxiety
- Drink water after the scan
Questions to Ask Your Doctor
- Do I have any allergy that matters?
- Should I change my diabetes medicines on the scan day?
- What snack should I bring?
- Who should I call if I feel unwell later?
Common Mistakes to Avoid
- Not telling the staff about diabetes or allergy.
- Skipping water after the scan.
- Ignoring a painful, swollen arm.
Booking, Timing and Report
Ask your doctor for the best timing of the scan. Book a morning slot so that fasting is easier, arrange someone to accompany you, and allow 2 to 3 hours at the centre. Carry biopsy, scan and blood reports and a medicine list. Reports are usually ready within 24 to 48 hours, and images can be given on a CD or digital link for your doctor.
After the Scan and Key Facts
After the scan, drink water, eat a light meal and rest if you feel tired. Most people return to work the same day. Keep your report and ask your doctor when the next scan is due. If you are worried about repeated PET CT scans, ask what each scan will add. Remember that the side effects of an untreated disease are usually much more serious than those of a well-planned scan.
Frequently Asked Questions
Does PET CT cause side effects?
Rarely. Most people feel nothing.
Can I be allergic to the tracer?
Extremely rare.
Is the scan painful?
No, only a needle prick.
Why do I feel dizzy?
Fasting can cause low sugar; tell the staff.
Can I drive after the scan?
Yes, unless you were sedated or feel dizzy.
Do I need to avoid people after PET CT?
Keep some distance from pregnant women and infants for a few hours.
What if I feel anxious?
Tell the staff. They can help you stay calm.
What if the injection site hurts?
Use a cold compress and tell your doctor if it worsens.
Can PET CT affect my medicines?
No, but ask about diabetes drugs on the day.
Book Your Test at Ganesh Diagnostic
Ganesh Diagnostic & Imaging Centre in Rohini, Delhi offers this test with trained radiology staff and clear reports. You can book an appointment online, check our branches across Delhi NCR, contact us for current rates, or explore all our services. Reports can be downloaded online through our patient portal, so you do not need to make a second trip just to collect them.
This article is for general information only. It does not replace advice from your doctor. Always follow your doctor's instructions for your test.
