Correlation between serum C3 and glomerular microthrombosis in patients with lupus nephritis

Objective To investigate the correlation between serum C3 and glomerular microthrombosis in patients with lupus nephritis (LN). Methods Patients who were diagnosed as LN by renal biopsy hospitalized in Department of Nephrology, the First Affiliated Hospital of Shenzhen University from January 2010 to February 2019 were retrospectively analyzed and they were divided into glomerular microthrombosis group (GMT group) and non-glomerular microthrombosis group (non-GMT group). The demographic data, clinical characteristics, pathology and prognosis of the two groups were compared. Logistic regression and smooth curve fitting of generalized additive mixed model analysis were used to explore the correlation between serum C3 and glomerular microthrombosis. Renal prognosis of the two groups were compared by the Kaplan-Meier survival curve. Results A total of 116 patients were enrolled, aged (32.79±11.43) years old, in which 108 cases (93.10%) were female. Thirty-seven patients (31.90%) were confirmed to be combined with GMT (GMT group) and 79 cases were not (non-GMT group). Compared with the non-GMT group, patients in the GMT group were relatively older (t=-2.876, P=0.002), with higher proportion of hypertension ( χ2=7.492, P=0.006)，higher urine protein quantitation (Z=-2.115, P=0.003), lower levels of eGFR and serum complement C3 (Z=3.469, P＜0.001; t=1.744, P＜0.001), higher systemic lupus erythematosus disease activity index (t=-2.758, P=0.007). As to the pathological characteristics, type IV LN patients were the majority (72.97%). Proportion of crescents and pathological activity indicators of the GMT group were higher (Z=-1.866, P=0.002; t=-5.005, P＜0.001), nuclear fragmentation, endothelial hyperplasia and renal tubular atrophy were more serious ( χ2=14.987, P＜0.001; χ2=15.695, P＜0.001; χ2=4.130, P=0.042). Multivariate logistic regression analysis indicated that serum complement C3 was a relational factor of the formation of GMT in LN patients (OR=0.966, 95％CI 0.938-0.995, P=0.023). Smooth curve fitting of generalized additive mixed model analysis indicated that level of complement C3 had a linear relationship with the changing trend of GMT. The Kaplan-Meier curve showed that there were statistical differences between the two groups in terms of complete remission of urine protein (Log-rank χ2=5.858, P=0.016) and doubled serum creatinine /end-stage renal disease (Log-rank χ2=3.945, P=0.047). Conclusions Serum C3 is closely related to the formation of GMT in LN patients, and statistical differences were demonstrated in the renal prognosis of GMT group and non-GMT group.