Anti-C1q antibodies may help in diagnosing a renal flare in lupus nephritis

It is still uncertain which, it any, immunologic parameters may help diagno se a renal flare of lupus nephritis. Anti-C1q antibody (Ab) titers have bee n elevated in patients with lupus with renal involvement, but little inform ation is available on whether the titers are different in quiescent and act ive phases of lupus nephritis. In this study, we compared anti-C1q Ab titer s with other serological test results in 48 patients with biopsy-proven lup us nephritis to assess which parameter could offer the best reliability for differentiating between quiescent end active phases of lupus nephritis. Se rum C3 and C4 levels, as well as anti-double-stranded DNA, antiendothelial cell, anti-C1q, and antiphospholipid Ab titers, were evaluated in patients with quiescent renal disease (38 samples) and those with clinical evidence of renal activity (23 samples). Only anti-C1q Ab titers correlated with act ive renal disease in both univariate (P < 0.0001) and multivariate analysis (P < 0.0001), with a sensitivity of 87% and a specificity of 92%. In six p atients, immunologic parameters were measured serially. In all patients, th e high anti-C1q Ab titers returned to normal values after treatment-induced remission. The other serological parameters did not show a significant ass ociation with renal disease activity. In patients with biopsy-proven lupus nephritis, anti-C1q Ab liters appear to be strongly related to renal diseas e activity. Their measurement may be useful for confirming the diagnosis of renal flares of lupus nephritis. (C) 2001 by the National Kidney Foundatio n, Inc.