The significance of serial measurements of serum complement C3 and C4 components and DNA binding capacity in patients with lupus nephritis.

Eighteen patients with systemic lupus erythematosus (SLE) and proliferative glomerulonephritis, underwent serial serum determinations of C3, C4, and native DNA binding capacity, as well as repeat renal biopsy 7 to 48 months (median 25 months) following initial biopsy. Highly significant correlations were found between serum C3 levels and renal histologic changes (P less than 0.0001), and between serum C3 levels and DNA binding capacity (P less than 0.03). Histologic deterioration correlated with depressed C3 levels, while improvement was associated with normalization of C3 levels. No correlation between renal histologic changes and either serum C4 levels or DNA binding capacity was found. The data suggest that the serum level of C3 is the best index of activity of lupus nephritis.