Factors That Change — Your SUV Reading

Not straightforwardly. SUV reflects how much tracer a tissue absorbed, not how aggressive the cancer is. Many non-cancerous conditions — inflammation, infection, healing tissue — can produce high SUV readings. Some cancers have naturally low uptake. Your oncologist interprets SUV alongside scan images, your clinical history, and other results. It is one input in a clinical picture, not a standalone score, and SUV alone does not diagnose cancer.

A rise in SUV can suggest increased metabolic activity, but it is only meaningful if the two scans were done under equivalent conditions. A difference in fasting, uptake time, or scanner calibration can produce a numerical rise with no change in the disease at all. Your radiologist and oncologist will assess the change together, accounting for scan conditions, before drawing any conclusion about disease behaviour.

The acceptable range is set by each scanning centre and the protocol it follows. You will be told the preparation requirements when your appointment is booked. On the day, your blood glucose is measured before the scan starts. If it was outside the acceptable range, the scanning team will decide whether to proceed or reschedule. Ask for your blood glucose reading on the day and whether the team was satisfied with it.

Some medications affect glucose metabolism and therefore FDG uptake. Insulin timing is the most common example: insulin given close to the scan time can redirect FDG into muscle rather than tumour tissue, which suppresses the reading. Always tell the scanning team about every medicine and supplement you are taking well before the appointment, so they can give you specific timing instructions for that day.

Each PET-CT scanner is calibrated independently, and small differences in calibration, uptake time, or image reconstruction settings produce real differences in SUV. This is a known limitation of the metric. It is one reason oncologists focus on the change in SUV within a single centre over time, rather than comparing raw numbers from different machines, when assessing how your disease is responding.

Different tissues have different baseline uptake. Brain, heart and kidneys show high physiological uptake; most other tissues show lower values at rest. What matters for cancer assessment is the uptake in a specific lesion relative to surrounding tissue and to previous scans at the same site, not a universal normal value. Your radiologist accounts for normal physiological uptake patterns when interpreting the scan.