Discontinuation of metformin to prevent metformin-induced high colonic FDG uptake: is 48 h sufficient?

OBJECTIVE: In this retrospective, single-center observational study, we investigated whether discontinuing metformin for at least 48 h prevents metformin-induced [(18)F]fluorodeoxyglucose (FDG) uptake in all segments of the colon. METHODS: Patients with type 2 diabetes who were using metformin before undergoing an FDG PET/CT scan were included. Two groups were created: patients who discontinued metformin for less than 48 h (< 48 h group) and patients who discontinued metformin for between 48 and 72 h (≥ 48 h group). A control group comprised non-diabetic patients who were not using metformin before undergoing an FDG PET/CT. We visually scored the uptake of FDG in four segments of the colon—the ascendens, transversum, descendens, and rectosigmoid—using a four-point scale (1–4) and considered scores of 3 or 4 to be clinically significant. RESULTS: Colonic FDG uptake in the ≥ 48 h group (n = 23) was higher than uptake in the control group (n = 96) in the colon descendens [odds ratio (OR) 14.0; 95% confidence interval (CI) 4.8–40.9; p value: 0.001] and rectosigmoid (OR 11.3; 95% CI 4.0–31.9; p value: 0.001), and there was no difference in the colon ascendens and transversum. Colonic FDG uptake in the < 48 h group (n = 25) was higher than uptake in the ≥ 48 h group (n = 23) in the colon transversum (OR 4.8; 95% CI 1.3–18.5; p value: 0.022) and rectosigmoid (p value: 0.023), and there was no difference in the colon ascendens and descendens. CONCLUSIONS: Discontinuing metformin for 48 h before undergoing an FDG PET/CT still gives a high uptake in the distal parts of the colon when compared with non-diabetic patients who are not using metformin. Discontinuing metformin for 48 h seems to be useful for scanning the more proximal segments of the colon.