How Long After an Infection — Should You Wait for a PET Scan?

Tell your oncology and nuclear medicine team about the infection before the scan is done — not at check-in, but when it is being arranged. A radiologist who knows about an active or recent infection writes the report differently, noting which findings may be infection-related and which need independent follow-up. Any area that cannot be confidently assigned to infection will still need tissue confirmation, so the scan is not wasted — it just needs the right context to be interpreted safely.

Six months after completing TB treatment is generally adequate for most people, provided you are fully recovered with no remaining symptoms. TB lymph node changes can persist on imaging for many months after clinical recovery even when the disease is fully treated, which is why completion of the full course — not just symptom resolution — is the clinical starting point. Bring your TB treatment completion records to the nuclear medicine appointment; the physician will confirm whether you are ready to proceed.

Any active infection can cause FDG uptake, not just chest and lymph node infections. A dental abscess, skin boil, or localised wound infection will show uptake in and around that area. Whether it matters for your scan depends on where the area is and what the cancer question is — a dental infection may not affect a scan focused on a pelvic tumour, but it could confuse a head and neck scan. Tell your nuclear medicine team about any recent infection, however minor it seems.

Completing the full course of TB treatment is the clinical standard before scanning, not just symptom resolution. TB can cause ongoing inflammatory activity in lymph nodes even after symptoms disappear, and that activity may still appear on the scan. Whether the cancer question is urgent enough to scan before treatment is complete is a clinical judgment that depends on your specific situation — this is a decision to make with your treating team rather than on your own.

It may be a partial explanation, but it cannot be confirmed from the image alone. An area of uptake near a recent infection raises two possibilities — it could be a false positive caused by inflammation, or it could be a finding that needs investigation in its own right, because cancer and infection can coexist. Any finding that cannot be confidently assigned to infection based on the full clinical picture needs tissue confirmation. Ask your oncologist what the next step is.

Call the nuclear medicine department before booking your appointment. Tell them what infection you had, when it started, when you recovered, and what treatment you received. They will advise whether you are ready to scan or how much longer to wait. No general guideline can substitute for that conversation, because the right wait depends on the type and severity of infection, how fully you have recovered, and how urgently the cancer question needs answering.