Validating a Scoring Tool to Predict Acute Kidney Injury (AKI) following Cardiac Surgery

Abstract

Background: Acute kidney injury (AKI) after cardiac surgery is associated with an increased risk of mortality. Preoperative risk scores can identify patients at risk for AKI and facilitate preventive strategies. Currently, validated risk scores are used to predict AKI requiring dialysis (AKI-D); less is known about whether these tools predict less severe forms of AKI. Objective: To evaluate the Cleveland Clinic scoring tool in predicting both AKI-D and less severe stages of AKI in patients after cardiac surgery in a Canadian tertiary care center. Design: Retrospective case-control study. Setting: Regina Qu'Appelle Health Region (RQHR) from 2007 to 2011. Patients: Patients who underwent cardiac surgery and developed postoperative kidney injury (n = 2316). Measurements: Data on risk factors for AKI and outcomes of cardiac surgery were collected from a retrospective chart review. Methods: The primary outcome was AKI, defined as Stage 1 (increase in serum creatinine 1.5–1.9 × baseline within 5 days), Stage 2 (increase 2.0–2.9 × baseline), or Stage 3 (increase 3.0 × baseline or more OR initiation of dialysis during hospital stay). We assessed the performance of a modified version of the Cleveland Clinic tool using receiver operating curve analyses. Results: The incidence of AKI was 6.1% (Stage 1), 2.6% (Stage 2), and 5.8% (Stage 3). The area under the curve (AUC) for the Cleveland score was 0.61 (95% CI: 0.56 to 0.65; p < 0.001) for Stage 1, 0.61 (95% CI: 0.54 to 0.68; p < 0.01) for Stage 2, and 0.78 (95% CI: 0.74 to 0.82; p < 0.001) for Stage 3. Greater level of risk on the Cleveland tool was associated with a higher risk of Stage 3 AKI. Limitations: Lack of prospective validation. Conclusions: The modified Cleveland Clinic tool was valid in identifying patients with severe stages of AKI but did not have strong discrimination for early AKI stages.