Kidney biopsy in lupus nephritis after achieving clinical renal remission: paving the way for renal outcome assessment

The role of repeat kidney biopsy in lupus nephritis (LN) with renal remission is unclear. The aim of this study was to assess this role in a real-life scenario. This retrospective, single-centre study included 56 patients with LN diagnosed from 1998 to 2019, with an initial kidney biopsy (KB1) at the onset of LN and a second kidney biopsy (KB2) after achieving renal remission. A total of 51 (91.1%) patients were women with a median age of 29.9 years [interquartile range (IQR) 23.4-40.6] at the time of LN diagnosis. KB2s were performed after 41.1 months (IQR 30.1-52.5) of KB1. At the time of KB2, complete renal response was achieved in 51 (91.1%) patients. The median activity index decreased from a baseline value of 6.5 (IQR 2.8-11) to 0 (IQR 0-2) (P < .001). The chronicity index worsened from 1 (IQR 0-2) to 2 (IQR 1-3) (P = .01). In patients with proliferative/mixed forms at KB2, the chronicity index median value increased to 3 (IQR 1.5-4), as well as interstitial fibrosis and tubular atrophy >= 25%, from 5.4% to 13.5%. Persistent histological active LN (activity index >= 2) was present in 11 (19.6%) KB2s. There were no differences when comparing immunological parameters between both groups (activity index >= 2 versus <2) at KB2, nor in the percentage of patients who presented renal flare. Immunosuppressive treatment was withdrawn in 35 (62.5%) patients and maintained/switched in 21 (37.5%). Afterward, new renal flare occurred in 9 patients per group (25.7% and 43%, respectively), after a median time of 39 months (IQR 6.5-55) and 7 months (IQR 6-30), respectively. There was no difference in the number of patients who developed chronic kidney disease [n = 14 (25%)] according to the treatment. In conclusion, KB2 provides valuable information to guide immunosuppressive maintenance therapy.