Laboratory Diagnosis Of Complement Component 1q And Cystatin C In Lupus Nephritis

Objective:To evaluate the values of serum urea?SUr?,creatinine?SCr?,cystatin C?CysC?,estimated glomerular filtration rate(eGFR_CysC,c-aGFR and eGFR_CKD-EPI)and complement component 1q?C1q?in the diagnosis of lupus nephritis?LN?.Methods:A total of 1316 outpatients and inpatients admitted to Mianyang Central Hospital,as well as healthy controls from the Physical Examination Center from March 2017 to December 2017 were selected.According to different disease types,the patients were divided into the following five groups:218 healthy controls?HC group?,339 SLE patients without renal involvement?SLE group?whose renal functions were determined as no impairment by the randomized urinary albumin to creatinine ratio?UACR?<30mg/g Cr,541 patients with other rheumatic immune diseases?ORID group?,148 patients with active LN?ALN group?and 70 patients with inactive LN?ILN group?.The levels of serum SUr,SCr,CysC and C1q were determined in each group.In addition,SUr/SCr,eGFR_CysC,c-aGFR and eGFR_CKD-EPI were calculated.The differences among the observed groups were analyzed.The correlations of these indicators in each group were analyzed by Spearman test.Fourfold-table risk analysis was evaluated to assess the risk degree of the abnormal rate of each indicator with LN.ROC curve was used to assess the performance of each indicator for diagnosing LN.Moreover,Logistic regression equations were used to find indicators closely associated with LN occurrence and make joint diagnosis.Results:?1?The differences of the observed indexes were statistically significant among all groups?P<0.05?.Pairwise comparison showed that there were significant differences between HC group and other groups in CysC?Z=-4.234^-14.988,P<0.001?,eGFR_CysC?LSD-t=4.237¹5.761,P<0.001?,eGFR_CKD-EPI?LSD-t=2.547¹2.978,P<0.05?,and C1q?LSD-t=4.583¹0.336,P<0.001?,except C1q between HC group and ORID group?LSD-t=-0.579,P=0.562?was similar.The differences of CysC?Z=-3.380^-7.587,P<0.01?,eGFR_CysC?LSD-t=4.138⁸.188,P<0.001?,and c-aGFR?LSD-t=3.600⁴.543,P<0.001?were statistically significant between SLE group and ALN group or ILN group or ORID group.The differences of C1q were statistically significant?LSD-t=5.295/-9.339,P<0.001?between SLE group and ALN group or ORID group,whereas there was no significant difference between SLE group and ILN group?LSD-t=0.222,P=0.824?.There was statistically significant difference in eGFR_CKD-EPIKD-EPI between SLE group and ALN/ILN group?LSD-t=11.269/4.302,P<0.001?,except the ORID group?LSD-t=-0.982,P=0.326?.There were statistically significant differences in C1q?LSD-t=-3.493,P<0.001?,eGFR_CysC?LSD-t=-2.046,P=0.041?and eGFR_CKD-EPI?LSD-t=-3.788,P<0.001?between ALN group and ILN group.?2?Spearman correlation analysis in each group showed that,C1q was positively correlated with SUr?r=0.151,P=0.025?and SUr/SCr?r=0.198,P=0.003?in HC group,while C1q was positively correlated with SCr?r=0.150,P=0.006?and negatively correlated with eGFR_CKD-EPI?r=-0.119,P=0.029?in SLE group.Additionally,C1q was positively correlated with SUr/SCr?r=0.092,P=0.033?and CysC?r=0.137,P=0.001?in ORID group.C1q in ALN and ILN groups was not correlated with all the observed indicators.?3?The risk analysis indicated that,except SUr/SCr,all the other observed indicators were risk factors of LN?P<0.05?.?4?The ROC analysis revealed that,among all observed indexes,eGFR_CysC/CysC?0.910?had the highest diagnostic performance?AUC?for diagnosing LN alone,followed by C1q?0.819?,eGFR_CKD-EPI?0.800?,SUr?0.671?,SCr?0.599?,c-aGFR?0.576?and SUr/SCr?0.564?.In other words,when tested separately,CysC/eGFR_CysC had the highest diagnostic performance,followed by C1q,and the difference between them was statistically significant?Z=3.12,P=0.002?.?5?Logistic regression analysis showed that when the other indicators were combined with the three different estimated eGFR,only C1q was closely related to LN in all three combinations.?6?The combination of C1q with one or more other indicators showed C1q+eGFR_CysC+eGFR_CKD-EPI had the best diagnostic performance?AUC=0.963,P<0.001?among all joint tests with sensitivity of 87%,and specificity of 95%,followed by C1q+eGFR_CysC?AUC=0.946,P<0.001?,with sensitivity of 87.7%,and specificity of 91.7%.The difference of the diagnostic performances between the two combined tests was statistically significant?Z=2.674,P=0.008?.Conclusions:?1?The differences between C1q and CysC in each group were statistically significant.In particular,the decrease of C1q level was most prominent in the ALN group,followed by the SLE group and the ILN group,and there was no significant change in the ORID group.?2?C1q showed little or no correlation with other observational indicators,and might be an independent risk factor of LN.?3?When tested separately,CysC or eGFR_CysC had the highest diagnostic performance for LN,followed by C1q.C1q+eGFR_CysC+eGFR_CKD-EPI was the optimal combined detection.Considering the economic reasons,C1q+eGFR_CysC combined detection could also achieve the similar optimal diagnostic performance.?4?Compared with c-aGFR and eGFR_CKD-EPI,the eGFR_CysC estimation equation in LN patients could reflect the patient's renal function state more accurately.