Brigham Research Institute (BRI) - Brigham and Women's Hospital

for Plasma Exchange-Treated Patients: 1. Adult (≥18 years old) 2. Either a new diagnosis of multiple myeloma confirmed by bone marrow plasmayctosis >10% or acute relapse of multiple myeloma 3. Light chain cast nephropathy, with involved light chain >500 mg/L 4. Acute kidney injury, defined as ≥1.5-fold rise in SCr from baseline (as defined in study outcomes) or the need for renal replacement therapy (RRT). 5. Treated with at least 1 round of plasma exchange within 30 days of diagnosis of cast nephropathy 6. Treated with plasma exchange in 2010 or later Inclusion Criteria for Control Patients: 1. Adult (≥18 years old) 2. Either a new diagnosis of multiple myeloma confirmed by bone marrow plasmayctosis >10% or acute relapse of multiple myeloma 3. Light chain cast nephropathy, with involved light chain >500 mg/L 4. Acute kidney injury, defined as ≥1.5-fold rise in SCr from baseline or the need for renal replacement therapy (RRT)

for Both Plasma Exchange-Treated Patients and Control Patients: 1. Patients with end stage kidney disease 2. Patients with amyloidosis or monoclonal immunoglobulin deposition disease 3. Patients with chronic lymphocytic leukemia, plasma cell leukemia, or Waldenstrom's 4. Moribund condition (e.g., patients who died within 48 hours of initiation of plasma exchange) 5. Active urinary tract obstruction on renal imaging 6. Patients with significant albuminuria (≥2+ on urinary dipstick or >10% fraction on UPEP) 7. Patients with other biopsy-proven causes of AKI (non-cast nephropathy lesions) 8. Patients who did not receive clone-directed therapy for myeloma 9. Patients who received plasma exchange >30 days from the time of diagnosis of cast nephropathy