Why Blood Sugar Changes — Your SUV Result

FDG and glucose compete for the same absorption pathways in your cells. If blood sugar is elevated, normal tissues absorb more of both, raising the background signal and making the scan harder to interpret accurately. Most centres follow EANM or Society of Nuclear Medicine guidance, which sets a threshold for when it is appropriate to proceed. Your pre-scan glucose level is also recorded so the radiologist knows the conditions under which the images were acquired.

Possibly. Any food raises blood sugar, which affects how FDG distributes through the body. If you ate before the scan, tell the team before the injection rather than after — they will check your glucose and decide whether to proceed or reschedule. If the scan has already been done, your oncologist needs to know so they can factor it into their reading. Hiding it creates a larger problem than rescheduling would have.

Practice varies by centre. Some reports include the pre-scan glucose in the clinical notes; others record it separately. It should have been checked before the injection. Ask your team to confirm what the reading was. If no glucose was measured, raise it with your oncologist — the radiologist was then interpreting the scan without knowing a condition that directly affects the result.

No, and this matters. SUV alone does not diagnose cancer and cannot confirm clearance. High uptake can occur in infection, inflammation, and other benign conditions. A low SUV on a scan done with elevated blood sugar may underestimate disease activity rather than reflect it. Your oncologist interprets the number within the full clinical picture — imaging pattern, your history, and comparison with previous scans. A number in either direction is not a conclusion on its own.

Some diabetes medications are paused before a PET scan and others are not. Insulin timing is also managed differently compared to a regular day. The answer depends on your specific medication and your centre's protocol. Ask the booking team when you confirm your appointment, not on the morning of the scan. Give them your medication list so they can provide the right instructions in advance.

A change in SUV is only meaningful when both scans were done under comparable conditions — similar glucose levels, similar fasting times, similar timing after injection, and on calibrated equipment. If one scan was done with high blood sugar and the next was not, the difference may reflect measurement conditions rather than a real change in the cancer. Ask your oncologist to confirm whether the conditions were comparable before drawing any conclusions from the comparison.