The relevance of complement levels in assessing the activity of lupus nephritis of different pathological types.

Objective: Systemic lupus erythematosus (SLE) is a chronic multisystem autoimmune disease that predominantly affects women of childbearing age. Lupus nephritis (LN) is a relatively common and serious complication in clinical patients. The aim of this study was to evaluate the correlation of complement levels and SLEDAI- 2000 (SLEDAI- 2 K) with renal activity in different pathological types of LN.

Methods: A total of 220 patients with SLE and LN were included. Renal active inflammation was calculated using the National Institutes of Health (NIH) Activity Index (AI) . Patients were classified into two groups based on the AI at the time of kidney biopsy: low-to-moderate-activity group with an AI < 10 and high-active group with an AI ≥ 10. Laboratory indicators, including complement levels and the SLEDAI- 2 K, were collected to assess their correlation with renal activity in LN.

Results: The average complement levels in class V LN were higher than that in class III/IV and III/IV + V LN. Serum creatinine and 24-h urine protein were lower than those in class III/IV and III/IV + V LN. Laboratory indicators, including complement levels and SLEDAI- 2 K, shown no correlation with AI in class V LN. Appropriate clinical indicators of AI in patients with class III/IV and III/IV + V LN were further assessed by ROC curves, SLEDAI- 2 K exhibiting the highest performance (AUC 0.757, 95% CI 0.687-0.817), 24-h urine protein (AUC 0.736, 95% CI 0.665-0.798), hemoglobin (AUC 0.726, 95% CI 0.655-0.789), C3 (AUC 0.676, 95% CI 0.603-0.744), serum creatinine (AUC 0.664, 95% CI 0.591-0.733), and C4 (AUC 0.660, 95% CI 0.586-0.729).

Conclusion: Decreased levels of complement C3 and C4 have limited predictive value as a clinical tool for assessing disease activity in patients with LN, especially in class V LN. SLEDAI- 2 K, a widely used clinical scale, correlates with disease activity in patients with class III/IV, III/IV + V LN. Serum creatinine is a clinical indicator of chronic kidney damage in patients with class III/IV, III/IV + V, and V LN. Key Points Complement levels: can they accurately assess disease activity in lupus nephritis? • Studies investigating the correlation between complement levels and disease activity in patients with SLE and LN yield inconsistent results, and the ambiguity of these findings may stem from factors such as the pathological staging of LN and individual variations in complement levels. Fewer studies in the current research on disease activity in patients with LN will be based on different pathological types of LN, which leads to limitations in the final findings. • This study aimed to analyze the feasibility of complement levels and SLEDAI- 2 K in assessing renal activity in patients with different pathological types of LN. • We assessed disease activity by obtaining AI from renal biopsies in 220 patients with LN and examined their correlation with disease activity through the collection of laboratory indicators from these patients. • Decreased levels of complement C3 and C4 have limited predictive value as a clinical tool for assessing disease activity in patients with LN, especially in patients with class V LN.