Serum alpha–actinin antibody status in systemic lupus erythematosus and its potential in the diagnosis of lupus nephritis

Background: In lupus nephritis (LN), deposition of pathogenic autoantibodies in the glomeruli is mediated via cross-reactivity with alpha-actinin. Association of serum alpha-actinin antibody (AαA) with LN has been shown in a few studies but the results are controversial. Methods: Eighty patients into entered the study. The diagnosis of SLE was confirmed according to the American College of Rheumatology criteria and LN was diagnosed by proteinuria ≥ 500 mg/24 hour and kidney biopsy. Serum AαA was measured with ELISA method. Receiver operating characteristics curve (ROC) analysis was applied to determine an optimal cutoff value for AαA to discriminate patients with and without LN at the highest sensitivity and specificity. The association of AαA with LN was determined by logistic regression analysis with calculation of odds ratio (OR). Results: Serum AαA was significantly lower in LN as compared with SLE patients without LN (P=0.001). Serum AαA at cutoff levels ≤ 59.5 pg/ml discriminated the two groups with sensitivity, specificity, positive predictive values of 60%. 90% and 85.7%, respectively. Serum AαA level ≤ 59.5 pg/ml was significantly associated with LN (OR=13.5, P=0.001) and the OR increased to 25.2 (P=0.003) after adjustment for age, sex, C3, C4, anti-ds-DNA, SLEDAI. Conclusion: This study indicates that serum AαA decreases in LN and serum level ≤ 59.5 pg/ml is SLE and is predictive of nephritis.