The Influence of Blood Glucose Levels on [18F]Fluorodeoxyglucose (Fdg) Uptake in Cancer: A Pet Study in Liver Metastases from Colorectal Carcinomas

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Abstract
Aims and background: To study the influence of blood glucose levels on the clinical reliability of positron emission tomography (PET) with [18F]-2-fluoro-2-deoxy-D-glucose (FDG) in the detection of liver metastases from colorectal carcinomas and in the analysis of tumor uptake of FDG. Methods: After having given their informed consent, 8 patients with 20 liver metastases (mean size, 31.5 mm; range, 10–75 mm) detected by means of CT were submitted to a first FDG-PET examination under fasting conditions and, 2 days later, to a second FDG-PET examination performed after iv infusion of a glucose solution (4 mg/kg/min for 2 hrs). The results of the two studies were compared in each patient, considering both the localization of the metastases and the FDG uptake in the lesions. A non-kinetic method was used, calculating the Standardized Uptake Value (SUV). Results: All 20 metastases were clearly visible on FDG-PET under fasting conditions. Moreover, in 2 patients FDG-PET detected a number of unknown liver metastases. The blood glucose levels after glucose infusion were significantly higher than the levels under fasting conditions, 158 ± 13.8 mg/100 ml (mean ± sd) and 92.4 ± 10.2, respectively (P « 0.001), and the quality of the FDG-PET images showed a marked deterioration. FDG-PET was unable to detect 6 of the 20 lesions and another 10 lesions were localized less clearly. Moreover, 80% of the unknown liver metastases were not detected after glucose loading. The SUVs of metastases decreased from 9.4 ± 5.7 (mean ± sd) under fasting conditions to 4.3 ± 8.3 after glucose loading (P « 0.001). Conclusions: FDG-PET studies may be particularly unreliable under conditions of high levels of blood glucose. Therefore, patients entering FDG-PET studies should fast, and blood glucose concentration needs to be taken into account when evaluating FDG uptakes in follow-up studies.