In multiple myeloma, which urine finding is classically present?

• A. Bence Jones proteins present in urine
• B. Red blood cell casts
• C. WBC casts
• D. Hematuria with RBC casts

Answer: (A)

In multiple myeloma, malignant plasma cells overproduce a single type of light chain, which are small enough to be filtered by the kidneys and excreted in urine as Bence Jones proteins. These free light chains can cause renal injury by forming casts with Tamm-Horsfall protein in the distal tubules, leading to myeloma kidney, and they may be detected even when routine dipstick protein tests are negative. Detection typically requires urine protein electrophoresis or immunofixation to identify the monoclonal light chains. The other urine patterns—red blood cell casts, white blood cell casts, or hematuria with RBC casts—are more indicative of glomerular or tubulointerstitial diseases, not the classic myeloma-associated finding. Therefore, the urine finding classically present is Bence Jones proteins in the urine.