Association between urine pH and risk of contrast-associated acute kidney injury among patients after emergency percutaneous coronary intervention: a V-shape relationship?

Aim We investigated whether perioperative urine pH was associated with contrast-associated acute kidney injury (CA-AKI) in patients undergoing emergency percutaneous coronary intervention (PCI). Methods The study enrolled 1109 consecutive patients undergoing emergency PCI. Patients were divided into three groups based on perioperative urine pH (5.0-6.0, 6.5- 7.0, 7.5-8.5). The primary endpoint was the development of CA-AKI, defined as an absolute increase >= 0.3 mg/dL or a relative increase >= 50% from baseline serum creatinine within 48 h after contrast medium exposure. Results Overall, 181 patients (16.3%) developed contrast-associated acute kidney injury. The incidences of CA-AKI in patients with urine pH 5.0-6.0, 6.5-7.0, and 7.5-8.5 were 19.7%, 9.8%, and 23.3%, respectively. After adjustment for potential confounding factors, perioperative urine pH 5.0-6.0 and 7.5-8.5 remained independently associated with CA-AKI [odds ratio (OR)1.86, 95% confidence interval (CI) 1.25-2.82, P = 0.003; OR 2.70, 95% CI 1.5-4.68, P < 0.001, respectively]. The association was consistent in subgroups of patients stratified by several CA-AKI risk predictors. However, the risk of CA-AKI associated with urine pH 7.5-8.5 was stronger in patients with worse renal function (estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73m(2)) (HR 5.587, 95% CI 1.178-30.599 vs. HR 2.487, 95% CI 1.331-4.579; overall interaction P < 0.05). Conclusion The urine pH and CA-AKI may underlie the V-shape relationship.