Based on the validation assays using independent serum samples and independent assay platforms, the serum levels of leukotriene B4, the lipid peroxidation marker MDA, gamma-glutamyl peptides or GGT, and glutathione emerge as excellent predictors of SLE, with superior specificity and sensitivity profiles (Fig. 4), effectively differentiating SLE from healthy controls as well as another pro-inflammatory, chronic systemic autoimmune disease, RA. Here, GGT1 is linked to rheumatoid arthritis.