A 68-year-old female presents with low-grade fever, myalgia, and bilateral lower extremity edema for 25 days, oliguria for 3 days, and hemoptysis for 1 day. Hemoglobin is 83g/L, urinalysis shows proteinuria, RBCs throughout the field of view, WBC count 20/HPF, 24-hour urinary protein quantification 3.7g, plasma albumin 29.6g/L, and serum creatinine 524μmol/L. To confirm the etiology, the preferred initial test is: