<s>[INST] context: Lupus nephritis is one manifestation of systemic problems related to immune complex deposition, including fever, arthralgias, myalgias, pancytopenia, and serositis with pericarditis and pleuritis, which are characteristic of systemic lupus erythematosus (SLE). Renal disease is common in SLE, and a renal biopsy helps to determine the severity of involvement and the appropriate therapy. Anti-centromere antibody is most specific for limited scleroderma (formerly CREST syndrome), which is unlikely to have renal involvement. Anti-DNA topoisomerase I antibody is more specific for diffuse scleroderma, which does have renal involvement, although usually, this manifests as vascular disease and not as glomerulonephritis. The anti-glomerular basement membrane antibody is characteristic of Goodpasture syndrome, in which the IgG antibody is deposited in a linear fashion along glomerular capillary basement membranes. Anti-histone antibody may be present in drug-induced lupus. ANCAs can be seen in some forms of vasculitis, such as ANCA-associated granulomatous vasculitis or microscopic polyangiitis. Antiribonucleoprotein is present in mixed connective tissue disease, which has some features of SLE but usually does not include severe renal involvement. [/INST] question: A 33-year-old woman has had fever and increasing fatigue for the past 2 months. Over the past year, she has noticed the soreness of her muscles and joints and has had a 4-kg weight loss. On physical examination, her temperature is 37.5degC, pulse is 80/min, respirations are 15/min, and blood pressure is 145/95 mm Hg. She has pain on deep inspiration, and a friction rub is heard on auscultation of the chest. Laboratory findings show glucose, 73 mg/dL; total protein, 5.2 g/dL; albumin, 2.9 g/dL; and creatinine, 2.4 mg/dL. Serum complement levels are decreased. CBC shows hemoglobin of 9.7 g /dL, platelet count of 85,000/mm3, and WBC count of 3560/mm3. A renal biopsy specimen shows diffuse proliferative glomerulonephritis with extensive granular immune deposits of IgG and C1q in capillary loops and mesangium. After being treated with immunosuppressive therapy consisting of prednisone and cyclophosphamide, her condition improves. Which of the following serologic studies is most likely to be positive in this patient? | options: A: Anti centromere antibody B: Anti-DNA topoisomerase I antibody C: Anti-double-stranded DNA antibody D: Anti-glomerular basement membrane antibody | answer: C </s>