Abstract 504: Cystatin-C Risk-Stratifies Patients for Acute Kidney Injury and 1-Year Major Vascular Events Following Contrast -Enhanced CT Imaging in the Emergency Care Setting

Background: Despite poor sensitivity in acutely ill patients, serum creatinine (and estimated glomerular filtration rate [eGFR SCR ]) remains the sole means of risk-stratifying patients for acute kidney injury (AKI) prior to contrast-enhanced CT imaging (CECT). Hypothesis: We hypothesized that an acute phase marker of renal dysfunction, cystatin-C (expressed as eGFR CYS ), would more accurately predict contrast-induced nephropathy (CIN) than eGFR SCR . Given the risk of arterial vascular events subsequent to AKI, we also evaluated eGFR CYS in risk-stratifying patients for major adverse events (MAE) within 1 year of CECT. Methods: We followed 462 consecutive adults, without end-stage renal disease, undergoing CECT (any indication) in the outpatient, emergency care setting for CIN and 1-year MAE: death, renal failure, myocardial infarction, stroke, and/or peripheral vascular event requiring intervention (blinded, adjudicated outcome). We excluded patients with life-threatening CECT indications and collected serum for eGFR SCR and eGFR CYS prior to CECT. Predictive accuracy was defined as the area under the receiver operating characteristic curve (AUROC) and likelihood ratios (LR+ and LR-). A threshold of ≤60 ml/min/m 2 defined an abnormal eGFR SCR or eGFR CYS . Results: CIN occurred in 14% and a MAE in 17% (low observer variability, κ>0.9) of our heterogeneous population: mean age 50 yrs (±16 yrs), 51% discharged after CECT, 16% with diabetes mellitus (DM), and only 16% with eGFR SCR ≤60ml/min/m 2 . CIN was associated with 1-year MAE: RR 2.4 (1.5-4.0) after adjusting for age and existing co-morbidities (active malignancy, CHF, DM, and CAD). The AUROC, LR+ and LR- for eGFR SCR were 0.55 (0.47-0.63), 0.9 (0.4-2.1) and 1.0 (0.9-1.1). In comparison, the AUROC, LR+, and LR- for eGFR CYS were 0.79 (0.62-0.96), 5.5 (3.9-7.6) and 0.43 (0.31-0.57), respectively. The MAE rate did not differ in patients with normal (13%) or abnormal (15%, p=0.5) pre-CECT eGFR SCR . Whereas, an abnormal eGFR SCR was associated with a 29% (p<0.01) increase in MAE. Conclusions: In patients undergoing CECT in the outpatient setting, eGFR CYS more accurately predicted CIN and more effectively risk-stratified patients for 1-year MAE than eGFR SCR . These findings warrant prospective validation.