A Retrospective Comparison of Creatinine Changes Among Patients Receiving, Not Receiving, and Not Yet Receiving Contrast Administration

Objective: We sought to compare variability in serum creatinine among inpatients in our institution receiving contrast imaging studies and among inpatients not receiving such studies. Materials and Methods: This retrospective, single-site, multiple-cohort study in a 550-bed academic medical center in October 2016 used the electronic medical record data to analyze the greatest absolute and relative changes in serum creatinine over periods no longer than 48 hours (1) during the admission for 1,134 patients who did not receive a contrast imaging study, (2) before the earliest contrast study for 155 patients who had not yet had a scheduled contrast examination, and (3) straddling the time when 266 patients received their earliest contrast study. We compared creatinine changes in the first cohort with those in the second and the third using histograms and t tests. Results: Among those who did not receive contrast, 18.3% had a creatinine increase of greater than 0.3 mg/dL, and before contrast, 14.2% had such increases (P =.22). After contrast, 6.4% had increases at least this great (P <.001). Patients with increases in creatinine before contrast tended to have such increases after as well (Pearson's 0.48, P <.001). Conclusions: Physiological variability may explain the similar increases among patients who did not receive contrast versus patients who had not yet received contrast. Hydration therapy may explain the milder and fewer increases after contrast. Only a randomized clinical trial can determine whether acute kidney injuries are caused by contrast; these results support equipoise for such a trial.