Clinical and histological features of lupus nephritis in Japan: a cross‐sectional analysis of the Japan Renal Biopsy Registry (J‐RBR)

Aim The clinical and histological features of lupus nephritis (LN) are highly variable, depending on race and ethnicity. The Japan Renal Biopsy Registry (J-RBR) is a nationwide registry of renal biopsies. Here, we report a cross-sectional analysis of Japanese LN using the J-RBR database. Methods Out of 18,463 patients registered in the J-RBR, 331 LN patients, who received renal biopsy for the first time, were extracted and their clinical features were analyzed according to the ISN/RPS 2003 classification. Results The median age of the 331 LN patients was 37 years old (women, 81.3%). The frequencies of each of the ISN/RPS Classes were as follows: I, 1.2%; II, 7.9%; III (±V), 25.1%; IV-S (±V), 13.0%; IV-G (±V), 31.1%; V, 20.8%; and VI, 0.9%. The level of proteinuria and the prevalence of nephrotic syndrome were highest for Class IV-G (±V). When Classes I, II, and VI were excluded from the analysis, Class IV-G (±V) was significantly associated with a lower eGFR and severer hematuria than the other classes. Conclusion This nationwide study revealed that Class IV-G (±V) was the most prevalent form of LN in Japan and was associated with a severe clinical renal presentation.