Influence of the blood glucose concentration on FDG uptake in cancer--a PET study

Radiolabeled [11F]-2-fluoro-2-deoxy-D-glucose (FDG) is a glucose analogue widely used to study tumor metabolism by means of positron emission tomography (PET). Little is known about the effect of hyperglycemia on FDG uptake and PET imaging of tumors. Five patients with head and neck cancer underwent two PET studies prior to cancer therapy, first in the fasting state and then 2-5 days later after oral glucose loading. FDG uptake was measured with standardized uptake values (SUV) and Ki values according to Patlak et al. The fasting SUVs ranged from 4.1 to 10.9 and Kis from 0.021 min-1 to 0.067 min-1, whereas after loading both the SUVs (range 2.2-5.9, p < 0.02) and Ki values (range 0.006-0.042 min-1, p < 0.05) decreased significantly, and the quality of the PET images became markedly poorer. The FDG metabolic rate (Ki x P-Gluc) remained similar in different plasma glucose concentrations in tumors, but increased clearly in muscles after loading. Therefore, patients entering PET-FDG studies should fast and their blood glucose concentration needs to be taken into account when evaluating FDG accumulation.