601568新浪(601568)

摘要：急性肾损伤(AKI, acute kidneyinjury)是临床常见的危重病症，常伴有不良预后和较高的病死率。该病以血清肌酐升高和尿量减少为诊断标准。近年来，随着基础医学研究的进步，发现了很多新型肾损伤标志物，其中NGAL和Cys-C被认为是AKI早期敏感标志物，对疾病的诊断、监测、预后等具有重要的意义。本文就NGAL和Cys-C在临床检验中的应用进行综述。

AKI，旧称急性肾衰竭(ARF,acute renal failure)，是一种临床常见的危重病症，以肾小球滤过率(GFR, glomerularfiltration rate)迅速下降为主要特征，临床以血清肌酐的升高和尿量减少为诊断标准。该病病死率高，预后差，并且发病率在全球呈上升趋势。在临床上，AKI亦缺乏有效的治疗手段，多以补液、营养支持或血管活性药物等辅助手段进行治疗，效果欠佳。因此，临床为降低AKI病死率主要以预防为主。

尽管AKI诊断标准经历了RIFLE、AKIN、KDIGO等几代的变迁，其分级依据依旧是以血清肌酐和尿量变化为主。而血清肌酐在AKI病程中又是个不敏感而且滞后的指标[1]，达不到风险评估和早期干预的目的，这也是导致AKI病死率居高不下的原因之一。

随着基础医学的不断深入研究，近年来发现一大批新的肾功标志物。其中中性粒细胞明胶酶相关载脂蛋白(NGAL, NeutrophilGelatinase-Associated Lipocalin)和胱抑素C(Cys-C, Cystatin C)的临床和学术研究较多，与AKI的关系也较为密切。本文主要以这两个肾功标志物进行详细阐述。

NGAL

NGAL最早是由Kjeldsen等人在1993年研究中性粒细胞MMP-9时发现的。该蛋白是一个分子量约为25kD的糖蛋白，由178个氨基酸残基组成，既能够自身聚合形成46kD的同源二聚体，也能够与MMP-9聚合形成135kD的异源二聚体。

在生理状态下，NGAL由中性粒细胞和某些上皮细胞（如肾小管上皮、支气管上皮等）微量表达。在缺血性或肾毒性肾损伤时，NGAL由肾脏大量表达，并被释放到尿液和血浆中。 研究者们发现，在动物肾损伤模型中，NGAL可分别在转录水平和翻译水平上调表达[2-5]。几项小型前瞻性研究数据显示，在体外循环术并发AKI患儿的病例中，患者在术后2-6小时内其血浆和尿液的NGAL水平即可升高，而血清肌酐则在AKI后的1-3天内升高[6-10]。2-6小时血浆和尿液NGAL水平作为诊断AKI的曲线下面积(AUC)＞0.9。而在另外一项涉及374例儿童体外循环的研究中，AKI患者的血浆和尿液NGAL在术后2小时即显著身高并至少维持48小时[11]。研究还显示，2小时的血浆和尿液NGAL水平与患者住院时间及AKI严重程度呈正相关。2-48小时的血浆和尿液NGAL水平作为诊断AKI的AUC在0.88-0.97之间[11]。在成人体外循环并发AKI的研究中，血浆和尿液NGAL水平(1-3小时)作为AKI诊断的AUC在0.61-0.96之间[12-18]。成人AUC数据较差的原因可能是因为病例较为复杂，如存在较多的老年病例、肾病患者、慢性疾病患者、糖尿病患者及手术时间延长病例等[19]。Haase-Fielitz等人的研究数据显示，在成人心脏手术并发AKI的病例中，血浆NGAL的AUC预测值要高于RIFLE和AKIN标准[17]。而McIlroy等的研究结果提示，心脏手术并发AKI的尿液NGAL水平与基础肾功能有关[20]。尽管各类研究得出的数据差别较大，meta分析心脏手术并发AKI的研究数据显示，术后6小时内的NGAL水平的平均AUC值为0.78(以血清肌酐升高＞50%定义为AKI)[21]。另外，造影剂、顺铂、环孢素等肾毒性物质引起的AKI病例中，患者血浆和尿液的NGAL水平亦显著升高[22-24]。

展开全文

Cys-C

Cys-C最早在1961年由Clausen发现，1985年首次被报道可作为评估GFR的指标。它是一种半胱氨酸蛋白酶抑制剂，广泛存在于各种组织的有核细胞和体液中，是一种低分子量（13.3kD）、碱性非糖化蛋白质，由122个氨基酸残基组成，可由机体所有有核细胞产生，产生率恒定。

相对于血清肌酐，Cyc-C基本不受年龄、种族、性别和肌肉含量影响，是非常好的GFR评价指标。一项涉及85例高危患者的研究中显示，AKI病例的血清Cys-C升高比血清肌酐早2天[25]。Delanaye和Villa等的研究结果也显示，血清Cys-C是优于血清肌酐的GFR和AKI早期诊断指标[26, 27]。Koyner等的研究结果还发现，在成人心脏手术并发AKI的病例中，6小时内的尿液Cys-C是良好的AKI诊断指标[13]。虽然Cyc-C是一个敏感的肾损伤指标，但不能良好区分慢性肾病早期损伤与AKI[28]，所以在临床应用中还需具体考虑患者基础肾功能水平。另外，近年的研究还显示，在肿瘤、甲状腺功能低下的患者中，血清Cyc-C含量也会变化[29-34]。

NGAL和Cys-C的联合检测

尽管NGAL和Cys-C在AKI的早期诊断中均表现良好，但依旧存在较大概率的误判。而且作为新型的肾损伤标志物，临床研究数据相对较少，这也是AKI诊断标准依旧使用血清肌酐的原因之一。

鉴于使用单一诊断指标可能出现较高漏诊率的局限性，临床上通常会联合使用两个以上的肾功标志物来提高AKI的检出率。例如在一项ST段抬高型心肌梗死并发AKI的研究中，作者联合检验NGAL和Cys-C，从而显著提高了AKI的检出率[35]。另外更多的研究显示，在不同的AKI研究样本中，肾功标志物的敏感性可能存在较大的差别。Arun等在评估糖尿病人心脏手术并发AKI的研究中显示，糖尿病组和对照组中血清Cyc-C升高均早于尿NGAL和血尿素氮，而糖尿病组的尿NGAL和血清Cys-C升高要早于血尿素氮和血清肌酐[36]。Herbert等的研究结果也提示，在体外循环术并发AKI 的婴幼儿(小于一周岁龄)中，血清Cys-C要敏感于尿NGAL[37]。而Ghonemy等在研究心脏手术并发AKI的数据中显示，血浆NGAL在AKI早期诊断中其准确度和敏感性均优于Cys-C[38]。在一项关于造影剂诱导的AKI研究中，血清NGAL在4小时出现峰值，到48小时基本回到正常值范围内，而血清Cys-C在24小时才出现峰值，但到48小时其浓度依旧维持在较高的水平[39]。所以，通过联合检测多个肾功标志物有助于降低临床AKI的漏诊率。

讨论

AKI以血清肌酐和尿量作为金标准的优点是确定性，不足是诊断的滞后性，从而贻误最佳治疗时间，这也是导致该病病死率高的原因之一。

虽然众多研究数据显示，可以通过联合检验的方式提高AKI的检出率，但是临床应用联合检测AKI的概率并不多。AKI诊断分级标准和检测费用也是制约联合检测发展的制约因素。

图1 肾损伤特异性标志物[40]

当然，联合诊断AKI也不仅限于NGAL和Cys-C，近年发现的肾功标志物还有很多，图1中Liborio整理了肾脏不同部位的生物标志物。其中每个标志物都有较多的基础临床数据支持。目前还没有发现单一完美的AKI诊断标志物，例如在严重烧伤并发AKI的患者中，血浆NGAL并不比血清肌酐升高的早[41]。笔者认为，在AKI诊断方面应该加大临床研究，联合检测多种肾功标志物，细分病患类别，提高AKI检出率和准确率，以免贻误最佳治疗窗口期，从而降低病死率，改善预后。

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