Objectives: To evaluate the role of immunological tests for monitoring lupus nephritis (LN) activity.
Methods: C3, C4, anti-dsDNA and anti-C1q antibodies were prospectively performed over 6 years in 228 LN patients.
Results: In membranous LN only anti-C1q antibodies differentiated proteinuric flares from quiescent disease (p=0.02). However, in this group 46% of flares occurred with a normal value of anti-C1q antibodies versus 20% in proliferative LN (p=0.02). In patients with antiphospholipid antibodies (APL), 33% of flares occurred with normal levels of anti-C1q antibodies versus 14.5% in APL-negative patients (p=0.02). In proliferative LN, anti-C1q antibodies showed a slightly better sensitivity and specificity (80.5 and 71% respectively) than other tests for the diagnosis of renal flares. All 4 tests had good negative predictive value (NPV). At univariate analysis anti-C1q was the best renal flare predictor (p<0.0005). At multivariate analysis, the association of anti-C1q with C3 and C4 provided the best performance (p<0.0005,p<0.005,p<0.005 respectively).
Conclusions: Anti-C1q is slightly better than the other tests to confirm the clinical activity of LN, particularly in patients with proliferative LN and in the absence of APL. All 4 "specific" tests had a good NPV, suggesting that, in the presence of normal values of each, active LN is unlikely.