RE: “Efficacy of oral contrast agents for upper gastrointestinal signal suppression in MRCP: A systematic review of the literature” by Frisch et al.

We read with interest the article by Frisch et al. (1). The use of negative oral contrast is an important technique in improving the visualization of the biliary tree and the authors’ review of this topic is timely. However, the findings of Frisch et al.’s review may have been limited by the lack of adherence to systematic methodology.

We note that in the current review there was no mention of prospective registration of the systematic review protocol. Further, only one database was searched and only full-text available studies included, a limitation explicitly acknowledged by the authors. Most importantly, there was no quality assessment performed on the included studies, a key component of a systematic review (2). Inconsistencies in the presentation of the quantitative results also impact on the understanding of the key findings, making verification of the conclusions difficult for readers. A table listing the studies with number of participants involved, type and details of oral contrast, and outcomes is expected in a systematic review involving such studies. In addition, a comment regarding in vitro assessment of oral contrast, a component of many included studies, would be necessary to outline how different investigators chose the type of oral contrast used in these studies.

The absence of several of the key features of a systematic review leads us to question whether the methodology of this study is more in keeping with an empirical review and whether a more rigorous systematic review is required to guide further clinical use of oral negative contrast agents in MRCP.