12-year-old Hispanic girl is seen in the clinic with her parents because of painful joints. History reveals that arthralgias started six months ago which affected both knee joints and all metacarpophalangeal joints of the left hand. She has associated fatigue and occasional fever. Physical examination reveals oral mucosal ulcers, discoid rash with malar distribution, and vasculitic rash on the toes. Complete blood count showed white blood count 6.1 x 109/L, neutrophils 4 x 109/L, bands 0.9 x 109/L, lymphocytes 0.5 x 109/L, monocytes 0.4 x 109/L, eosinophils 0.3 x 109/L, and platelets 84 x 109/L. Which of the following tests is most specific for the diagnosis of the patient's condition?
-Anti-ribonucleoprotein antibody
-Anti-Smith antibody
-Antihistone antibodies
-Antinuclear antibody (ANA)
