AI Overview · plain answer
FDG-avid means a spot on your PET scan took up more of the sugar tracer (FDG) than the tissue around it. Many cancers do this, but so do infection, TB, inflammation and healing tissue, and some normal organs.[1]
So FDG-avid is a finding, not a diagnosis. Doctors decide what the spot is by combining the PET with the CT picture, your history, earlier scans and, often, a biopsy.
Important
This page explains what the words in a PET-CT report mean in general. It is patient education, not medical advice. It cannot tell you what a spot on your own scan is. Please discuss your report with the doctor who is treating you.
What ‘FDG-avid’ means
FDG (fluorodeoxyglucose) is a sugar-like substance with a small amount of radioactivity attached. It is injected into a vein before the scan. Cells take it up in the same way they take up sugar, and it stays inside them long enough for the scanner to see it.[1]
Cells that are working hard use more sugar, so they collect more FDG and show up brighter. A spot that is brighter than the tissue around it is called FDG-avid. The word describes how active the spot is. It does not say what the spot is.
What else can make a spot FDG-avid?
Cancer is one cause. It is not the only one. These are the common reasons a spot can light up on an FDG PET scan:[1]
| What it can be |
Why it lights up |
What helps tell it apart |
| Cancer |
Many cancers use a lot of sugar |
Shape and size on the CT, the pattern of spots, change over time, biopsy |
| Infection, including TB |
Cells fighting infection use a lot of sugar |
Symptoms, blood tests and biopsy. TB and cancer can look the same on PET[3] |
| Inflammation |
Active inflammation uses sugar |
The pattern of spots, other scans, biopsy |
| Healing tissue after surgery, a biopsy or radiotherapy |
Healing tissue is active |
The dates of recent treatment; a later scan |
| Lymph nodes after a vaccine |
Nodes react to the vaccine, usually on the side of the injection |
The date of the vaccine and the arm it was given in[6] |
| Normal organs and muscles |
The brain, heart, kidneys, bladder and bowel, busy muscles, and ‘brown fat’ in the cold |
The reader knows these normal patterns[1] |
Why this matters in India
TB is common in India. In one Indian study of single lung nodules, TB and cancer took up similar amounts of FDG.[3] In another, from Delhi, PET often called chest lymph nodes abnormal when a needle biopsy (EBUS) found no cancer in them.[4] A bright spot on PET therefore often needs a biopsy before anyone can say what it is.
Words and numbers in the report
Reports use several phrases for the same idea. FDG-avid, hypermetabolic, increased FDG uptake and increased metabolic activity all mean the spot took up more tracer than its surroundings.
Most reports also give an SUV (standardised uptake value), often written as SUVmax. It is a number for how much tracer the spot took up. SUV changes with the scanner, the time between the injection and the scan, and your blood sugar, so there is no single SUV that means cancer.[1][2] An SUV is most useful when it is compared with your own earlier scan, done in a similar way.
When a cancer is not FDG-avid
The opposite also happens. Some cancers take up little FDG, so a report may say a spot is non-FDG-avid even when it needs attention. In gastric cancer, for example, FDG PET found peritoneal spread (spread to the lining of the abdomen) much less often than FAPI PET in pooled studies.[9]
For some cancers, doctors prefer a different PET tracer: PSMA PET for prostate cancer[7] and somatostatin-receptor PET (such as DOTATATE or DOTATOC) for well-differentiated neuroendocrine tumours.[8] FAPI PET is newer; a 2025 SNMMI/EANM guideline says it has no approved clinical indications yet.[10]
What usually happens next
- Your doctor compares the PET with the CT picture, your symptoms, blood tests and any earlier scans.
- A biopsy may be advised. A sample is usually needed to confirm cancer, TB or another cause: most often a biopsy, and for TB sometimes a sputum or fluid test. The PET can show which spots are most active.
- Or a repeat scan after some weeks, to see whether the spot changes.
- You can ask for a second reading of the scan by another specialist.
How often does a second reading change the opinion?
In one US cancer-centre study of 240 PET-CT scans done at other centres, specialist re-reading gave a different opinion about cancer for 31 scans (13%). Where the final answer was later known, the re-read was right in 25 of 28 of those cases.[5] In that study, most re-reads agreed with the first report about cancer; for about 1 scan in 8, the specialist’s opinion was different.
PET-CT Second Read · an independent reading of your scan
If your report says a spot is FDG-avid and you are unsure what it means, Dr. Ishita B. Sen and Dr. Dharmender Malik, nuclear medicine physicians at TPPL, Gurugram, would be happy to review the scan itself. You receive a structured, digitally signed report within 72 hours of us receiving the complete scan and information. The fee is ₹2,500 for patients in India and USD 100 for international patients. The report is written to be shared with your treating doctor.
You will need: a DICOM link of the PET-CT (most scan centres give one on request), the original report, any earlier scans, a biopsy report if you have one, and a short clinical summary. How the Second Read works →
Request a Second Read · WhatsApp +91 8800 988936
When a Second Read can’t help
- It cannot replace a biopsy. A reading of the scan, however expert, cannot confirm cancer or TB; that needs a sample.
- It needs the actual images (a DICOM link), not only the PDF report.
- It cannot fix a scan done in the wrong conditions, for example with very high blood sugar. A repeat scan may be needed.
- It is not for emergencies. New severe pain, breathlessness, weakness or bleeding needs your doctor or a hospital now.
- It does not replace your treating doctor. The report is written for them to use.
For patients & families
Frequently asked questions
Q01Does FDG-avid mean I have cancer?
Not on its own. FDG-avid means the spot took up more of the sugar tracer than the tissue around it. Cancer often does this, but so do infection, TB, inflammation and healing tissue. Your doctors decide what the spot is by looking at the CT picture, your history, earlier scans and, often, a biopsy.
Q02Is a higher SUV always worse?
Not necessarily. SUV is a number for how much tracer a spot took up. It changes with the scanner, the timing of the scan and your blood sugar, so there is no single number that means cancer. In one Indian study of lung nodules, TB and cancer had similar SUVs. SUV is most useful when compared with your own earlier scan done in a similar way.
Q03My report says the uptake is mild or low. Is that good news?
It cannot be read on its own. Mild uptake can come from inflammation or healing tissue, but some cancers also take up only a little FDG. Ask your doctor how the finding fits with the CT picture and your other tests.
Q04Can TB look like cancer on a PET scan?
Yes. TB is active tissue and can take up as much FDG as cancer. In Indian studies, TB and cancer in lung nodules took up similar amounts of FDG, and PET often called chest lymph nodes abnormal when a biopsy found no cancer. This is why a biopsy is often needed where TB is common.
Q05Why has my doctor asked for a biopsy after the PET scan?
A PET scan shows how active a spot is, not what it is. A sample is usually needed to confirm cancer, TB or another cause: most often a biopsy, and for TB sometimes a sputum or fluid test. If a biopsy is needed, the PET can show which spots are most active.
Q06Can diabetes or high blood sugar affect the result?
Yes. High blood sugar can reduce how much FDG a tumour takes up. The European (EANM) guideline says a routine scan can go ahead when blood sugar is below 11 mmol/L (about 200 mg/dL); at or above this level the scan is usually rescheduled. Do not stop or change your diabetes medicines on your own; follow the scan centre's written instructions.
Q07What does non-FDG-avid mean?
It means the spot took up little or no FDG. It is not the same as benign: some cancers take up little FDG. For some cancers, doctors use a different PET tracer, such as PSMA PET for prostate cancer.
Q08Can I get my PET scan read again by another specialist?
Yes. The PET-CT Second Read service reviews a scan you already have. You send a DICOM link of the scan, the original report, any earlier scans, a biopsy report if you have one and a short clinical summary. The fee is ₹2,500 for patients in India and USD 100 for international patients. The report is sent within 72 hours of receiving complete information, and it is written to be shared with your treating doctor.
Evidence & references
[1] Boellaard R et al. FDG PET/CT: EANM procedure guidelines for tumour imaging, version 2.0. Eur J Nucl Med Mol Imaging 2015 (PMID 25452219) — patient preparation, blood-sugar limits, normal FDG uptake, and factors that change SUV.
View source ↗[2] Adams MC et al. A systematic review of the factors affecting accuracy of SUV measurements. AJR Am J Roentgenol 2010 (PMID 20651185).
View source ↗[3] Purandare NC et al. Indian J Cancer 2017 (PMID 29199704) — FDG PET/CT for solitary lung nodules in a region where TB is common.
View source ↗[4] Gupta M et al. Eur J Nucl Med Mol Imaging 2026 (PMID 42249940) — PET-CT compared with EBUS needle biopsy for chest lymph nodes in locally advanced lung cancer, in a TB-endemic group in Delhi.
View source ↗[5] Ulaner GA et al. Nucl Med Commun 2017 (PMID 28291158) — specialist re-reading of 240 PET-CT scans performed at other centres.
View source ↗[6] Becker AS et al. Radiology 2021 (PMID 33625298) — recommendations for imaging lymph nodes after COVID-19 vaccination.
View source ↗[7] EAU–EANM–ESTRO–ESUR–ISUP–SIOG Guidelines on Prostate Cancer (2025) — use of PSMA PET.
View source ↗[8] Hope TA et al. Appropriate use criteria for somatostatin receptor PET imaging in neuroendocrine tumors. J Nucl Med 2018 (PMID 29025982).
View source ↗[9] Ruan D et al. Theranostics 2023 (PMID 37649615) — meta-analysis of FAPI PET in gastric cancer, including peritoneal spread.
View source ↗[10] Hope TA et al. SNMMI Procedure Standard/EANM Practice Guideline for Fibroblast Activation Protein (FAP) PET. J Nucl Med 2025 (PMID 39572227).
View source ↗
About the Author
Dr. Ishita B. Sen
MBBS · DRM · DNB (Nuclear Medicine) · Senior Director & Head, Department of Nuclear Medicine and Molecular Imaging
Dr. Sen leads the nuclear medicine and theranostics programme in Gurugram, with a focus on PSMA and DOTATATE imaging and Lu-177 and Ac-225 radioligand therapy. Together with Dr. Dharmender Malik, she reviews the PET-CT scans sent to the Second Read service.