Renal Functional Recovery Confounding the Assessment of Contrast Nephropathy: Propensity Score Analysis

Background: Large data analyses confirm the relative safety of contrast-enhanced computed tomography (CT), except for those with advanced renal failure. However, the prevalence of post-contrast acute kidney injury may be masked by acute kidney functional recovery (AKR) in unstable inpatients, irrespective of contrast-enhanced imaging. Methods: In this work we aimed to assess AKI and AKR along with need for dialysis and mortality, among inpatients undergoing contrast-enhanced or non-enhanced CT. We performed a large-scale retrospective data analysis using propensity score matching (PSM) that compared patients undergoing contrast-enhanced and non-enhanced imaging. We also performed a subgroup analysis of subjects stratified by baseline renal function. Results: A total of 41,456 patients were analyzed. PSM resulted in well-balanced groups. AKR occurred substantially more often than AKI among hospitalized patients following CT imaging, especially among those with low baseline renal function. Yet, in this population, whereas the rate of AKI significantly increased, the rate of AKR significantly decreased following contrast-enhanced studies as compared to patients that underwent non-enhanced CT. A significantly higher proportion of patients with baseline advanced renal failure that underwent contrast-enhanced imaging required dialysis. Conclusions: The increased incidence of AKI and AKR as seen in patients with lower pre-imaging kidney function possibly suggests that both entities reflect impaired renal functional reserve. Unstable kidney function in inpatients, as demonstrated by rates of AKR and AKI, is an important confounder which requires attention in similar observational studies on the renal effects of contrast media and of various other renal injurious events.