Laboratory diagnosis of lupus nephritis by complement component 1q and cystatin C

Abstract:

Objective：To investigate the value of serum urea（Urea），creatinine（Creat），cystatin C（CysC），estimated glomerular filtra－tion rate（eGFRCysC and c-aGFR），and complement component 1q（C1q） in the diagnosis of lupus nephritis（LN）. Methods：A total of 560 patients with systemic lupus erythematous（SLE） who were admitted to our hospital from March to December，2017 were enrolled as subjects. In those patients，339 had the kidney uninvolved（SLE group），150 active LN（LNA group），and 71 inactive LN （LNI group）. Additionally，360 healthy individuals were used as controls（HC group）. Serum levels of Urea，Creat，Urea/Creat，CysC，and C1q were measured. eGFRCysC and c-aGFR were calculated to evaluate the diagnostic performance of these indices for LN. Results：There was a significant difference in each index between these groups（all P=0.000）. Spearman correlation analysis showed that C1q was not correlated with Creat，Urea，or Urea/Creat（r=0.046，P=0.160；r=0.011，P=0.748；r=-0.011，P=0.743），but negatively correlated with CysC，eGFRCysC，and c-aGFR（r=-0.183，P=0.000；r=-0.183，P=0.000；r=-0.075，P=0.023）. CysC was positively correlated with Urea and Creat（r=0.309，P=0.000；r=0.382，P=0.000），negatively correlated with c-aGFR（r=-0.430，P=0.000），but not correlated with Urea/Creat（r=0.003，P=0.927）. The analysis of the diagnostic performance of individual index for LN by re－ceiver operating characteristic curve revealed that eGFRCysC and CysC had the largest area under the curve（AUC=0.891，0.890），followed by C1q，Urea，Urea/Creat，c-aGFR，and Creat（AUC=0.804，0.660，0.630，0.547，0.501）. The maximum diagnostic performance was achieved by combined measurement of C1q，CysC，and c-aGFR，with a sensitivity of 89.3% and a specificity of 93.1%（AUC=0.962，YI=0.824）. The diagnostic performance was not further im－proved by increasing the number of indices. Conclusion：For the diagnosis of LN by a single index，CysC or eGFRCysC has the best diagnostic performance，followed by C1q. For the diagnosis by multiple indices，C1q，CysC，and c-aGFR are the optimal combination. Combined measurement of C1q and CysC is a more economic approach without comprising the optimal diagnostic performance.