Intravenous Contrast in Patients With Diabetes on Metformin

New Common Sense Guidelines

Arti D. Shah, MD; Cody McHargue, BA; Judy Yee, MD; Robert J. Rushakoff, MD

Endocr Pract. 2016;22(4):502-505.

Exceptions

We believe there remain some possible exceptions to the new guidelines. Metformin leads to intense, diffusely increased fluorodeoxyglucose (FDG) uptake in the colon, and to a lesser degree, the small intestine, which limits the diagnostic capabilities of FDG positron emission tomography (PET)/CT scanning and may mask gastrointestinal malignancies.^[16] The authors point out that this may leave some intestinal cancers or metastatic bowel lesions undetected, potentially resulting in incorrect cancer staging and inability to detect second primary cancers and assess therapeutic responses. This masking is unrelated to the administration of IV contrast. It is therefore recommended that metformin should be discontinued 48 hours before FDG PET/CT scanning in oncology patients to optimize scan sensitivity for malignancy detection. Unfortunately, as elevated plasma glucose can directly compete for uptake with radiolabeled glucose, there may be decreased sensitivity of the test in patients with elevated glucose (in this case as a result of metformin discontinuation). In this case, patients may require additional antihyperglycemic agents after metformin discontinuation to maintain reasonable glycemic control.^[16]

We applaud the new guidelines from the ACR. They reflect the current data that do not show any significant risk of AKI in patients with normal baseline renal function or an eGFR ≥30 mL/min/1.73 m² who are taking metformin and having an IV contrast procedure; therefore, there is no need to discontinue metformin before or after IV contrast and no obligation to check renal function after the exam. Finally, common sense prevails.

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Abbreviations
ACR = American College of Radiology; AKI = acute kidney injury; CT = computed tomography; Cr = creatinine; DM = diabetes mellitus; eGFR = estimated glomerular filtration rate; FDA = Food and Drug Administration; FDG = fluorodeoxyglucose; IV = intravenous

Acknowledgment
We appreciate the statistical analysis assistance of Isabel Allen, PhD; and assistance with data collection by Priyanka Jha, MD and Donald Chau, BS.
Dr. Shah was supported by a National Institutes of Health (NIH) training grant (5T32DK007418-34) and the Wilsey Family Foundation. Dr. Yee was supported by an NIH grant (RO1CA181191) and Echopixel. The study was supported by UCSF-CTSI grant number UL1 TR000004.

Table 1. 2015 American College of Radiology Manual on Contrast Media (7)
Iodinated Contrast Category I. (eGFR ≥30 mL/min/1.73 m²) In patients with no evidence of AKI and with eGFR ≥30 mL/min/1.73 m², there is no need to discontinue metformin either prior to or following the intravenous administration of iodinated contrast media, nor is there an obligatory need to reassess the patient's renal function following the test or procedure. Category II. (eGFR <30 mL/min/1.73 m²) In patients taking metformin who are known to have AKI or severe chronic kidney disease (stage IV or stage V; i.e., eGFR <30 mL/min/1.73 m²), or are undergoing arterial catheter studies that might result in emboli (atheromatous or other) to the renal arteries, metformin should be temporarily discontinued at the time of or prior to the procedure, withheld for 48 hours subsequent to the procedure, and reinstituted only after renal function has been re-evaluated and found to be normal. Gadolinium-based contrast material It is not necessary to discontinue metformin prior to contrast medium administration when the amount of gadolinium-based contrast material administered is in the usual dose range of 0.1 to 0.3 mmol/kg body weight.