The short answer
A PET scan uses a radioactive tracer that settles in areas of your body with high levels of chemical activity. MedlinePlus says cancer cells show up as bright spots, but bright spots can also signal other conditions.
A PET scan uses a radioactive tracer that settles in areas of the body with high levels of chemical activity.
MedlinePlus says cancer cells show up as bright spots on a PET scan, but bright spots can also signal other conditions.
A bright area on its own does not tell you the cause. Ask your care team what they think it most likely is.
Follow your preparation instructions. MedlinePlus lists fasting 4 to 6 hours and avoiding tobacco, caffeine and alcohol for 24 hours, and says to tell your provider about all medicines and supplements.
On this page
Choose how you want to read this
The whole article, with every detail and caution.
This page is for anyone whose PET scan report mentions "uptake" or an SUV number. It explains what the scan measures, why many things besides cancer light up, and what to ask.
What a PET scan is actually measuring
MedlinePlus says a PET scan uses a radioactive tracer that settles in areas of your body that have high levels of chemical activity. Those areas show up as bright spots on the images.
What bright spots can mean
MedlinePlus says cancer cells show up as bright spots on a PET scan, but bright spots can also signal other conditions. That is why a report describing an area of uptake is not, by itself, a diagnosis of cancer. Your care team looks at the result together with your other tests and history.
Preparing for the scan
MedlinePlus says to fast for 4 to 6 hours beforehand, avoid tobacco, caffeine and alcohol for 24 hours before, and tell your provider about all medicines and supplements. If you have diabetes and take insulin, talk with your provider about timing. Tell your provider if you are worried about being in a small space, since sedation may be possible. Follow the instructions your imaging center gives you.
Reading your report with your team
Has a report left you with a finding and no explanation? The most useful question is not what the number means. Ask what your team thinks the area most likely is, and what would happen next. Call your care team right away about new or worsening symptoms, whatever your scan showed.
Sources
Common questions
The report says an area is hypermetabolic. Does that mean cancer?
Not by itself. Hypermetabolic means the area has higher chemical activity than the tissue around it. MedlinePlus says cancer cells show up as bright spots, and bright spots can also signal other conditions. Ask your care team what they think the area most likely is and what happens next.
What does SUV mean?
SUV is a number some reports use to describe how much tracer has gathered in an area. It is a measurement, not a diagnosis. Ask your care team what any change in it means for you.
How should I prepare for the scan?
MedlinePlus says to fast for 4 to 6 hours beforehand, avoid tobacco, caffeine and alcohol for 24 hours before, and tell your provider about all medicines and supplements. If you have diabetes and take insulin, talk with your provider about timing. Follow the instructions your imaging center gives you.
Can a PET scan miss cancer?
A scan result is one piece of information. Ask your care team whether other tests are needed, and call your care team right away about new or worsening symptoms whatever your scan showed.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
More words from this kind of report
Other guides in scan & imaging reports.
Talk with a trained specialist or navigator
Cancer Explained provides educational guidance, but does not replace trained specialists, social workers, or your medical team.
Talk to a trained cancer information specialist
Free, confidential assistance from NCI Cancer Information Service via phone, chat, or email.
Contact your oncology team
Locate after-hours contact numbers, portal messages, or urgent triage phone lines.
Find a patient navigator
Get one-on-one help with appointments, logistics, translation, and care coordination.
Find a genetic counselor
Discuss inherited mutation risk, family history, and genetic testing options.
Find an oncology social worker
Access emotional counseling, family support groups, and mental health resources.
Find a financial navigator
Locate copay assistance foundations, grant programs, and lodging/travel support.
Find a clinical-trial specialist
Search matching studies and speak with NCI trial information specialists.
Get urgent help
Fever of 100.4°F (38°C) or higher during chemo, severe pain, or trouble breathing: call your cancer care team right away, day or night. Call 911 for an emergency.
Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Written by: Cancer ExplainedSources last checked: 2026-10-16 what this meansLast updated: 2026-10-16Next planned review: 2027-07-30
Review details and limits
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status — Source checked. This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
General education — varies by person. Answers genuinely differ between people. This page explains what commonly varies and points you to your care team for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Words to know
Tap any term to see what it means.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Read more about our editorial process, our use of AI, and our corrections policy.
Spotted a problem? Report an error — a factual mistake, broken or outdated source, confusing wording, or anything that seems unsafe. Please do not include names, medical record numbers, dates of birth, addresses, or other identifying medical information in your report.
After using this page, do you understand what to do next?
Anonymous — we only record the answer, never who gave it.