P13 Assessing the ability of Anti-C1q antibody measurement to predict a flare of lupus nephritis

Background Patients with lupus nephritis (LN) are at risk of relapse and hence long term disease monitoring is required. Here we undertook a prospective follow up of patients after having Anti-C1q antibodies (C1Q Ab) measurement to determine whether the result predicted a flare of LN. Methods SLE patients attending an Inner-City Lupus Center, were involved in the study. A point-in-time measurement of C1Q Ab was made using an ELISA kit (Orgentec Diagnostika GmbH). Medical records of patients were reviewed over the following 1 year to identify LN flares. A renal flare was defined as a doubling of the protein creatinine ratio with a subsequent decision to escalate immunosuppressive therapy. Results 116 lupus patients were included in the study. Of those, 52 had biopsy proven LN (45%). Positive C1Q ab was more common in patients with a history of biopsy proven LN (n=17, 32.7%) compared to those with non-renal SLE (n=10, 15.6%), (p=0.03). Renal flares tended to be more common in C1q ab positive LN patients (n=4, 26.7%) compared to those without C1q ab (n=2, 7.14%). (p=0.782). Of the 64 patients with non-renal SLE, 1 (10%) C1Q Ab positive patient subsequently developed LN compared with 1 (1.85%) C1Q Ab negative patient (p=0.173). There was no correlation between the level of C1Q Ab and the rate of LN flares. Conclusion C1Q Ab has a known correlation with LN, however, its ability to predict flares has been less well characterized. Our prospective analysis shows that although the C1Q Ab positive patients were more likely to have a flare of LN in the following year, there was not a statistically significant difference between the C1Q Ab positive and negative groups. In addition, only a relatively small proportion of C1Q Ab positive patients went on to have a flare (20%). Our data therefore does not support the use of C1Q Ab in predicting a flare of LN.