Proposed step-wise algorithm for the diagnosis of MGRS. *Renal biopsy advised if ≥1 of acute kidney injury (AKI) stage 3, estimated glomerular filtration rate (eGFR) < 60 mL/min per 1.73 m2 and >2 mL/min per 1.73 m2 per year decline, proteinuria and hematuria, albumin/creatinine ratio > 30 mg/mmol, and FS (hypouricemia).9 *Renal biopsy considered if ≥1 of AKI stage 1 or 2, eGFR < 60 mL/min per 1.73 m2 and <2 mL/min per 1.73 m2 per year decline, albumin/creatinine ratio 3 to 30 mg/mmol and eGFR > 60 mL/min per 1.73 m2, hematuria and eGFR < 60 mL/min per 1.73 m2, and evidence of light chain proteinuria.9 *Defer renal biopsy if stable eGFR, bland urinalysis, and no evidence of light chain proteinuria.9 In ∼40% of cases, monoclonal protein is not demonstrated in serum/urine. In such cases, renal biopsy should be considered in the diagnostic algorithm depending on the clinical suspicion.3 In cases of MGRS-compatible renal lesion with monoclonal immunoglobulin deposition, a diagnosis of MGRS should be considered and therapy instituted, because a monoclonal protein might not be demonstrated in some of these cases, despite a thorough evaluation (eg, PGNMID, FG). The latter situation could arise due to the extremely small amount of monoclonal protein that escapes detection by conventional methods or a result of pitfalls in the current diagnostic assays. IEM, immunoelectron microscopy; IF, immunofluorescence; LMD, laser microdissection; TM, tandem mass spectrometry. Adapted from Leung et al9 with permission.