On a pet scan is SUV 5.2 high? Very high or average?

SUV. Roughly....Mild uptake is usually SUV 1 - 3, Moderate 3-5, and Intense 6+.
Higher than normal. The Standard Uptake Value (SUV) on a PET/CT is used to measure the metabolic activity in a structure. It is normal for the SUV in the liver to be between 5 and 6. The SUV in the urinary system will also be very high because the agent used in this type of study is excreted in the urine. In other tissues, if a structure demonstrates an SUV above 2.5 it is concerning for cancer or infection.
PET scans. PET scans measure the uptake of a labeled sugar by cells (SUV = standardized uptake value). Generally, above 2.5 is considered high. I cannot comment on high vs very high. High SUV can occur in cancer, but also in active inflammation and some other ailments. Therefore, what an abnormal PET scan means depends on the clinical situation/whole picture; best not to interpret the results yourself.