A 50-year-old woman with SLE presents to the emergency depament with complaints of headache and fatigue. Her past manifestations of SLE have been ahralgias, haemolytic anaemia, malar rash, and mouth ulcers, and she is known to have high titres of antibodies to dsDNA. She currently is taking prednisone, 5 mg daily, and hydroxychloroquine, 200 mg daily. On examination, she is found to have a BP 190/110 mmHg with a HR 98 bpm. A urinalysis shows 25 RBCs per HPF with 2+ proteinuria. No RBC casts are identified. Her BUN is 90 mg/dL, and creatinine is 2.8 mg/dL (baseline 0.8 mg/dL). She has not previously had renal disease related to SLE and is not taking NSAIDs. She denies any recent illness, decreased oral intake, or diarrhoea. What is the most appropriate next step in the management of this patient?