The information concerning non-invasive, easily obtainable, and accurate biomarkers for diagnosis of lupus nephritis (LN) is extremely limited. The aim of this study was to evaluate the diagnostic performance of cystatin C (CysC) and complement component 1q (C1q) for LN. A case-control study that included 905 patients with systemic lupus erythematosus (SLE) without LN (group SLE), 334 patients with active lupus nephritis (group LNA), 255 patients with inactive lupus nephritis (group LNI), and 497 healthy individuals (group HC) was performed in Mianyang Central Hospital from March 2017 to December 2018. The serum levels of CysC, C1q, urea (Urea), and creatinine (Creat) were measured, and 2 estimated glomerular filtration rates (eGFRCysC and eGFRCreat) were calculated by equations which were based on serum CysC established by our group and the modification of diet in renal disease (MDRD), respectively. ANOVA analysis or Kruskal-Wallis test was used for comparing the differences among the groups, and receiver operating characteristic (ROC) curve was applied to identify the diagnostic efficiencies of individual or combined multiple indicators. Significantly elevated CysC and decreased C1q were observed in the LNA and LNI groups, which was in contrast to their levels in the SLE and HC groups. CysC (AUC = 0.906) or eGFRCysC (AUC = 0.907) assessed the highest diagnostic performance on LNA when detected individually, followed by C1q (AUC = 0.753). Joint utilization of C1q and CysC achieved very good performance (AUC = 0.933) which approximated to the best one observed in the combinations of C1q, Urea, CysC, eGFRCreat, and Creat (AUC = 0.975). The separately detected CysC (eGFRCysC) and C1q were superior to the conventional biomarkers Urea, Creat, and eGFRCreat in the diagnosis of LNA. Moreover, although the combined detection of Urea, Creat, C1q, CysC, and eGFRCreat had the greatest diagnostic performance, the joint utilization of CysC and C1q could be prioritized for rapid discrimination of LNA if the economic burden is taken into consideration.

中文翻译：

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血清胱抑素 C 和补体成分 1q 对狼疮性肾炎的诊断性能

有关用于诊断狼疮性肾炎 (LN) 的非侵入性、易于获得且准确的生物标志物的信息极其有限。本研究的目的是评估半胱氨酸蛋白酶抑制剂 C (CysC) 和补体成分 1q (C1q) 对 LN 的诊断性能。一项病例对照研究，包括 905 例不伴 LN 的系统性红斑狼疮 (SLE) 患者（SLE 组）、334 例活动性狼疮性肾炎患者（LNA 组）、255 例非活动性狼疮性肾炎患者（LNI 组）和 497 名健康个体（ 2017年3月至2018年12月在绵阳市中心医院进行，测定血清CysC、C1q、尿素（Urea）、肌酐（Creat）水平，并计算2种估计肾小球滤过率（eGFRCysC和eGFRCreat）通过分别基于我们组建立的血清CysC和肾病饮食调整（MDRD）的方程。采用ANOVA分析或Kruskal-Wallis检验比较组间差异，并应用受试者工作特征（ROC）曲线来确定单个或多个指标组合的诊断效率。LNA 和 LNI 组中观察到 CysC 显着升高，C1q 显着降低，这与 SLE 和 HC 组中的水平形成鲜明对比。CysC (AUC = 0.906) 或 eGFRCysC (AUC = 0.907) 在单独检测时评估了 LNA 的最高诊断性能，其次是 C1q (AUC = 0.753)。C1q 和 CysC 的联合使用取得了非常好的性能（AUC = 0.933），接近于 C1q、Urea、CysC、eGFRCreat 和 Creat 组合中观察到的最佳性能（AUC = 0.975）。单独检测的CysC（eGFRCysC）和C1q对LNA的诊断优于常规生物标志物Urea、Creat和eGFRCreat。此外，虽然Urea、Creat、C1q、CysC和eGFRCreat的联合检测具有最佳的诊断性能，但如果考虑到经济负担，可以优先考虑CysC和C1q的联合检测来快速区分LNA。