Renal, Urology and Electrolytescommon
A 36-year-old woman with systemic lupus erythematosus has increasing ankle swelling and foamy urine. Her urine protein-to-creatinine ratio is 180 mg/mmol (reference range less than 15), urine microscopy shows red-cell casts, complement levels have fallen and serum creatinine has risen from 75 to 125 micromol/L. Which investigation is most appropriate to determine the renal lesion and guide immunosuppressive treatment?