Between 2006 and 2013, there were 2583 patients that met their inclusion criteria. They found that there was no statistical difference overall between incidence of AKI in the contrasted study group vs. the non-contrasted study group. They also found that there was no statistical difference between the need for dialysis following contrasted studies and non-contrasted studies. When sub-divided by baseline GFR (which was determined by pre-study BMP), they found no statistical difference in incidence of AKI or the need for dialysis in any of the sub-groups after receiving either a contrasted or non-contrast study.

Overall, we felt this was a well designed study, and felt their approach to examining the effect of contrasted studies on patients with varying degrees of underlying kidney disease was well executed. The results tend to mirror some of the larger retrospective cohorts performed in the radiology, nephrology, and now emergency medicine literature.

One of the key drawbacks to this study, and many of the similar articles published recently on this topic, is that they are all retrospective cohort studies. This is due to the fact that it would be unethical to prospectively randomize a patient to receive a sub-optimal study for their disease process. As a result, there exists a large selection bias which may underestimate the true incidence of contrast induced nephropathy (AKI and dialysis secondary to IV contrast use).

Another aspect of the study that is important to recognize, and the authors do a good job highlighting this in their own discussion section, is that the number of patients with a GFR of 15-29 and <15 were too low to draw any conclusions. The confidence intervals for these groups were as high as 20-25, making it impossible to draw any conclusion for these groups. Data for patients with a GFR > 30 however, was well powered enough to say that there was no statistical difference in incidence of AKI and need for dialysis between contrast enhanced and non-contrast studies.

Our take away from this study is that for patients with patients with decent kidney function (GFR > 30) the incidence of AKI and dialysis is fairly low, and we can possibly be more liberal with our use of contrast in these patients. However, the incidence is not 0, and there does appear to be a trend of increasing incidence with worsening underlying kidney function. Though this was not statistically significant between contrasted and non-contrast studies, the n for patients with GFR < 30 was extremely low making it difficult to trust the results in this subgroup. Therefore, we cannot ignore a patient’s kidney function completely, and we should still exercise caution when considering contrasted studies in patients with moderate to severe underlying kidney disease.