Urine microscopy as a biomarker of Acute Kidney Injury following cardiac surgery with cardiopulmonary bypass

Abstract Introduction: Acute kidney injury (AKI) occurs in about 22% of the patients undergoing cardiac surgery and 2.3% requires renal replacement therapy (RRT). The current diagnostic criteria for AKI by increased serum creatinine levels have limitations and new biomarkers are being tested. Urine sediment may be considered a biomarker and it can help to differentiate pre-renal (functional) from renal (intrinsic) AKI. Aims: To investigate the microscopic urinalysis in the AKI diagnosis in patients undergoing cardiac surgery with cardiopulmonary bypass. Methods: One hundred and fourteen patients, mean age 62.3 years, 67.5 % male, with creatinine 0.91 mg/dL (SD 0.22) had a urine sample examined in the first 24 h after the surgery. We looked for renal tubular epithelial cells (RTEC) and granular casts (GC) and associated the results with AKI development as defined by KDIGO criteria. Results: Twenty three patients (20.17 %) developed AKI according to the serum creatinine criterion and 76 (66.67 %) by the urine output criterion. Four patients required RRT. Mortality was 3.51 %. The use of urine creatinine criterion to predict AKI showed a sensitivity of 34.78 % and specificity of 86.81 %, positive likelihood ratio of 2.64 and negative likelihood ratio of 0.75, AUC-ROC of 0.584 (95%CI: 0.445-0.723). For the urine output criterion sensitivity was 23.68 % and specificity 92.11 %, AUC-ROC was 0.573 (95%CI: 0.465-0.680). Conclusion: RTEC and GC in urine sample detected by microscopy is a highly specific biomarker for early AKI diagnosis after cardiac surgery.

摘要：约22%接受心脏手术的患者会发生急性肾损伤 (Acute kidney injury, AKI)，其中2.3%需要接受肾脏替代治疗 (renal replacement therapy, RRT)。当前基于血清肌酐水平升高的AKI诊断标准存在局限性，新型生物标志物 (biomarker) 的相关研究正在开展。尿沉渣 (urine sediment) 可作为一种生物标志物，有助于区分肾前性（功能性）与肾性（内在性）AKI。
研究目的：探讨尿液沉渣显微镜检查在接受体外循环心脏手术患者的AKI诊断中的应用价值。
研究方法：本研究纳入114例患者，平均年龄62.3岁，男性占比67.5%，基线血清肌酐水平为0.91 mg/dL（标准差0.22）。所有患者均在术后24小时内留取尿液样本进行检测，寻找肾小管上皮细胞 (renal tubular epithelial cells, RTEC) 与颗粒管型 (granular casts, GC)，并将检测结果与按照改善全球肾脏病预后组织 (Kidney Disease: Improving Global Outcomes, KDIGO) 标准定义的AKI发生情况进行关联分析。
研究结果：按照血清肌酐标准，共有23例患者（20.17%）发生AKI；按照尿量标准，则有76例患者（66.67%）发生AKI。其中4例患者需要接受RRT，总体死亡率为3.51%。以血清肌酐相关指标预测AKI时，灵敏度为34.78%，特异度为86.81%，阳性似然比为2.64，阴性似然比为0.75，受试者工作特征曲线下面积 (Area Under the Receiver Operating Characteristic curve, AUC-ROC) 为0.584（95%置信区间 (95% confidence interval, 95%CI)：0.445~0.723）。以尿量标准预测AKI时，灵敏度为23.68%，特异度为92.11%，AUC-ROC为0.573（95%CI：0.465~0.680）。
研究结论：尿液样本经显微镜检测发现的RTEC与GC可作为心脏手术后早期AKI诊断的高特异性生物标志物。