MRCP2-4647
A 42-year-old woman presents with fatigue, loss of appetite, gradual weight loss, and occasional chest pain. She also reports a rash on her nose and cheeks that worsens in the summer and joint pain in her wrists, knees, and ankles. On examination, her blood pressure is 150/94 mmHg, and she has a facial rash. Her test results show a low hemoglobin level, low white blood cell count, low platelet count, prolonged partial thromboplastin time, elevated C-reactive protein, high sodium and potassium levels, elevated creatinine, and blood and protein in her urine. What is the most specific test to determine her underlying diagnosis?