Is the presence of a solitary kidney an independent risk factor for acute kidney injury after contrast-enhanced CT?

Purpose: To determine whether patients with a solitary kidney are at higher risk for contrast material-induced acute kidney injury (AKI) than matched control patients with bilateral kidneys. Materials and Methods: This retrospective study was HIPAA compliant and approved by the institutional review board. Adult patients with bilateral kidneys or a solitary kidney from unilateral nephrectomy who underwent contrast material-enhanced computed tomography (CT) at this institution from January 2004 to August 2013 were identified. The effects of contrast material exposure on the rate of AKI defined as an increase in maximal observed serum creatinine (SCr) level of either (a) ≥0.5 mg/dL (44.2 mmol/L) or (b) ≥0.3 mg/dL (26.52 mmol/L) or 50% over baseline within 24-72 hours of exposure and 30-day post-CT emergent dialysis and death were determined after propensity score-based 1:3 matching of patients with solitary kidneys and control patients with bilateral kidneys. Differences in clinical characteristics and outcomes between the solitary and bilateral kidney groups were assessed by using the Wilcoxon rank sum test or Pearson x2 test prior to matching and by using conditional logistic regression after matching. Results: Propensity score matching yielded a cohort of 247 patients with solitary kidneys and 691 patients with bilateral kidneys. The rate of AKI was similar between the solitary and bilateral kidney groups (SCr ≥ 0.5 mg/dL AKI definition odds ratio = 1.11 [95% confidence interval {CI}: 0.65, 1.86], P = .70; SCr ≥ 0.3 mg/dL or 50% over baseline AKI definition odds ratio = 0.96 [95% CI: 0.41, 2.07], P = .99). The rate of emergent dialysis was rare and also similar between cohorts (odds ratio = 1.87 [95% CI: 0.16, 16.4], P = .61). Although the rate of mortality was higher in the solitary kidney group (odds ratio = 1.70 [95% CI: 1.06, 2.71], P = .0202), chart review showed that no death was attributable to AKI. Conclusion: Our study did not demonstrate any significant differences in the rate of AKI, dialysis, or death attributable to contrast-enhanced CT in patients with a solitary kidney versus bilateral kidneys.