AI Overview · plain answer
The SUV (standardised uptake value) is a number for how much of the PET tracer a spot took up. A higher SUV means a more active spot. It does not say what the spot is.[1]
There is no single ‘cancer range’. The number changes with the scanner, the timing of the scan and your blood sugar.[1][2] In an Indian study of lung spots, cancers and TB spots had overlapping SUVs, so an SUV of 8 or 18 can be cancer or TB.[3] Other infection and inflammation can also read high.[1] The SUV is most useful when compared with normal tissue in the same scan and with your own earlier scan done the same way.
Important
This page explains what the SUV number means 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 the SUV measures
Before a PET scan, a small amount of a sugar-like tracer (FDG) is injected. Busy cells take up more of it. The SUV compares the amount of tracer in a spot with the amount there would be if the tracer were spread evenly through the whole body, based on the dose given and your body weight.[1] An SUV of 1 means about the same as an even spread. An SUV of 8 means about eight times as much.
Reports usually give SUVmax, the value of the brightest single point in the spot. Some also give SUVmean (the average over the spot) or SUL, an SUV corrected for lean body weight, which the European guideline recommends giving alongside the SUV.[1]
What to compare it with
An SUV means little on its own. Doctors who read the scan compare a spot with normal tissue in the same scan. The European (EANM) guideline gives these examples:[1]
| Normal tissue |
Usual SUV |
| Blood in the main blood vessel (aorta) |
About 1.6 |
| Liver |
Mean about 2 to 3; maximum about 3 to 4 |
| Brain, heart, kidneys and bladder |
Can be high, and this is normal |
So an SUV of 8 or 18 is clearly higher than normal liver: the spot is active. That still does not tell you why it is active.
If you have lymphoma
Lymphoma scans done during and after treatment are often reported with a 5-point scale (the Deauville score) instead of the SUV alone. It compares the most active area of lymphoma with the blood in the chest and the liver. A score of 1 means no uptake, 3 means above the blood but not above the liver, and 5 means much higher than the liver or new spots. An international lymphoma panel recommends this scale for reporting.[5]
Why there is no cancer range
The European guideline says there is no single lower limit of FDG uptake that marks a spot as abnormal.[1] The same spot can give different numbers for reasons that have nothing to do with what it is:
| What changes the SUV |
Why it matters |
| Time from injection to scan |
The guideline recommends 60 minutes (55 to 75 accepted), and the actual time should be recorded[1] |
| Blood sugar |
High blood sugar can make cancers show up less clearly[1] |
| The scanner and its settings |
Different machines and settings can give different numbers for the same spot[2] |
| Size of the spot |
Very small spots can read lower than they really are[1] |
| Breathing |
Movement can blur spots in the lungs[1] |
| Type of tumour |
Some cancers take up a lot of FDG and some very little[1] |
Most importantly, infection, TB and inflammation can reach the same numbers as cancer. In a Tata Memorial study of 191 lung spots, cancers had SUVs from 3.3 to 34.6 and TB spots from 2.7 to 22.5, with no clear difference between them.[3] An SUV of 8, or of 18, sat inside both ranges. Read more: lymph node on PET, TB or cancer? →
The old ‘2.5 rule’
An SUV of 2.5 is sometimes quoted as a dividing line between cancer and not cancer in lung spots. The Tata Memorial study tested this line:[3]
- About two in three spots that were not cancer (65%) were above 2.5.
- About 5 in 100 cancers (5.5%) were below 2.5.
So a number above 2.5 does not prove cancer, and a number below it does not rule cancer out.
Comparing with an earlier scan
The SUV is most useful for following the same spot over time, for example before and after treatment. For a fair comparison, the European guideline says the repeat scan should use the same scanner and settings and the same time from injection to scan, within 10 minutes.[1][2] If your two scans were done at different centres or on different machines, the numbers may not be directly comparable.
Small changes can come from the scan itself. PET response criteria used by specialists (PERCIST) look for a fall of at least 30%, measured in a set way, before calling it a response.[4] Your doctor will also look at the size of the spots and whether any new ones have appeared.
Questions to ask your doctor
- What do you think the spot is, looking at the whole scan and not only the number?
- How does it compare with my liver and with the rest of the scan?
- Is there an earlier scan to compare with? Was it done on the same machine, in the same way?
- Was my blood sugar within the limit for the scan on the day, and was the time from injection to scan recorded?
- Do I need a biopsy or another test to know what the spot is?
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.[6] Most re-reads agreed with the first report.
PET-CT Second Read · an independent reading of your scan
If you are worried about an SUV number in your report, Dr. Ishita B. Sen and Dr. Dharmender Malik, nuclear medicine physicians at TPPL, Gurugram, would be happy to review the scan itself. The report explains what the spots look like against normal tissue in the same scan and against any earlier scans you send. 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 turn an SUV into a diagnosis. A PET-CT reading cannot prove cancer or TB on its own; that usually needs a sample (biopsy).
- It cannot make the SUV numbers from two scans directly comparable if the scans were done on different machines or in different ways. Your doctor will decide if a repeat scan is needed.
- It needs the actual images (a DICOM link), not only the PDF report.
- 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
Q01What is a normal SUV on a PET scan?
There is no single normal number. Doctors compare a spot with normal tissue in the same scan. The European (EANM) guideline gives the liver as an example: a mean SUV of about 2 to 3 and a maximum of about 3 to 4. Blood in the main blood vessel reads about 1.6. The brain, heart, kidneys and bladder can read high, and this is normal.
Q02Is an SUV of 18 cancer?
Not necessarily. An SUV of 18 means the spot is very active, but cancer, TB and other infection or inflammation can all reach high numbers. In an Indian study of lung spots, cancers had SUVs from 3.3 to 34.6 and TB spots from 2.7 to 22.5, so an SUV of 8 or 18 sat inside both ranges. A biopsy is often needed.
Q03Is an SUV below 2.5 safe?
Not always. Some cancers take up little FDG, and small spots can read lower than they really are. In the same Indian study, about 5 in 100 cancers had an SUV below 2.5, and about two in three spots that were not cancer had an SUV above it. The 2.5 rule on its own is not reliable.
Q04What is SUVmax?
SUVmax is the SUV of the brightest single point in a spot. It is the number most reports give. Some reports also give SUVmean (the average over the spot) or SUL (the SUV corrected for lean body weight).
Q05My SUV went from 10 to 7. Is my treatment working?
It may be. That is a fall of 30%. PET response criteria used by specialists (PERCIST) look for a fall of at least this size, measured in a set way. But the two numbers can only be compared fairly if both scans were done on the same scanner, with the same settings and about the same time between the injection and the scan. Your doctor will also look at the size of the spots and whether any new ones have appeared.
Q06Can high blood sugar change my SUV?
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.
Q07Does a higher SUV mean the cancer is worse or more advanced?
Not on its own. The SUV does not give the stage of a cancer. How much FDG a tumour takes up depends partly on the type of tumour: some take up a lot and some very little. Your doctors judge how serious a cancer is from its type, where it has spread and other tests, not from the SUV alone.
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) — how SUV is measured, normal reference values, uptake time, blood-sugar limits and repeat scans.
View source ↗[2] Adams MC et al. A systematic review of the factors affecting accuracy of SUV measurements. AJR Am J Roentgenol 2010;195:310–320 (PMID 20651185).
View source ↗[3] Purandare NC et al. Indian J Cancer 2017 (PMID 29199704) — FDG PET/CT for 191 solitary lung nodules in a region where TB is common (Tata Memorial Centre, Mumbai).
View source ↗[4] Wahl RL et al. From RECIST to PERCIST: evolving considerations for PET response criteria in solid tumors. J Nucl Med 2009;50 Suppl 1:122S–150S (PMID 19403881).
View source ↗[5] Barrington SF et al. Role of imaging in the staging and response assessment of lymphoma: consensus of the International Conference on Malignant Lymphomas Imaging Working Group. J Clin Oncol 2014;32:3048–3058 (PMID 25113771).
View source ↗[6] Ulaner GA et al. Nucl Med Commun 2017 (PMID 28291158) — specialist re-reading of 240 PET-CT scans performed at other centres.
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.