Elevated uric acid increases the risk for acute kidney injury.

BACKGROUND: Uric acid has been proposed to play a role in acute kidney injury. We therefore investigated the potential influence of preoperative serum uric acid (SUA) on acute kidney injury in patients undergoing cardiovascular (CV) surgery. The primary aims were to investigate the incidence of acute kidney injury, peak serum creatinine (SCr) concentrations, hospital length of stay, and days on mechanical ventilation.

METHODS: Retrospective study included patients who underwent CV surgery and had preoperative SUA available. Acute kidney injury was defined as an absolute increase in SCr ≥0.3 mg/dL from baseline within 48 hours after surgery. Univariate and multivariate logistic regression analysis was performed to determine the odds ratio for acute kidney injury.

RESULTS: There were 190 patients included for analysis. SUA were divided into deciles. The incidences of acute kidney injury were higher with higher deciles of SUA. When the incidences of acute kidney injury were plotted against all available values of SUA at increments of 0.5 mg/dL, a J-shaped curve emerged demonstrating higher incidences of acute kidney injury associated with both hypo- and hyperuricemia. In the univariate analysis, SUA ≥5.5 mg/dL was associated with a 4-fold (odds ratio [OR] 4.4; 95% confidence interval [CI], 2.4-8.2), SUA ≥6 mg/dL with a 6-fold (OR 5.9; 95% CI, 3.2-11.3), SUA ≥6.5 mg/dL with an 8-fold (OR 7.9; 95% CI, 3.9-15.8), and SUA ≥7 mg/dL with a 40-fold (OR 39.1; 95% CI, 11.6-131.8) increased risk for acute kidney injury. In the multivariate analysis, SUA ≥7 mg/dL also was associated with a 35-fold (OR 35.4; 95% CI, 9.7-128.7) increased risk for acute kidney injury. The 48-hour postoperative and hospital-stay mean peak SCr levels also were higher in the SUA ≥5.5 mg/dL group compared with the SUA <5 mg/dL group. SUA ≥7 mg/dL was associated with increased length of hospital stay (SUA <7 mg/dL, 18.5 ± 1.8 days vs SUA ≥7 mg/dL, 32.0 ± 6.8 days, P = 0.058) and a longer duration of mechanical ventilation support (SUA <7 mg/dL, 2.4 ± 0.4 days vs SUA ≥7 mg/dL, 20.4 ± 4.5 days, P = 0.001).

CONCLUSION: Preoperative SUA was associated with increased incidence and risk for acute kidney injury, higher postoperative SCr values, and longer hospital length of stay and duration of mechanical ventilation support in patients undergoing cardiac surgery. A J-shaped relationship appears to exist between SUA and acute kidney injury.