Background and aims The aim of this study was to review renal flare frequency, to identify potential risk factors for relapses, to assess the value of serological tests during flares and to analyse their impact of global outcome in lupus nephritis (LN) patients.

Methods Patients with biopsy proven LN were identified from our database. LN classes were defined according to the ISN/RPS classification. According to the response to treatment, LN patients were divided into 3 groups of complete remission (CR), partial remission (PR) and no response (NR). Those in remission were divided into 2 groups of relapsing and non-relapsing during maintenance period.

Results 218 (70,64%) of 276 SLE patients with biopsy proven LN (class I-18 patients, class II-45, class III-56, class IV-75, class V-54, class VI-2, mixed forms - 26) achieved either CR (55,8%) or PR (23,2%). 47 patients had one flare, 36 - two, 27 - three, 17≥4 flares. The maintenance immunomodulating drugs at the time of flare was low dose corticosteroids and/or azathioprine. Non-adherence to treatment at time of relapse was documented in 26 patients.

Conclusions Renal flares in patients with LN are common, have a negative impact on outcome, but cannot be readily predicted. Our study shows that 58,83% of LN patients develop at least one relapse after reaching remission, usually within 2 years. The length of time to flare tends to be shorter in cases of preceding PR than in CR. Lack of adherence to long term immunosuppression was identified as a significant factor in LN flare (20,47%).