A 24-year-old female patient had sore throat and fever 6 months ago. Two days later, she developed gross hematuria throughout urination, with mild urinary frequency and dysuria. Two weeks ago, she had another episode of gross hematuria with low back pain after a cold. BP is 130/80 mmHg, urinary protein (++), and sediment shows RBCs throughout the field of view. Which test is most helpful for identifying glomerular-origin hematuria?