Renal intratubular casts Intratubular light-chain casts The presence of casts containing immunoglobulin light chains within the lumina of the renal tubules. This feature can be ascertained by (i) Light microscopy: The biopsy shows chronic tubulointerstitial nephritis with fractured casts that first involve the distal tubules. The casts have a metachromatic appearance due to their mixed composition of light chain (Bence-Jones) and Tamm-Horsfall (uromodulin) proteins. Surrounding cellular reaction can extend to formation of syncytial giant cells, and in the early phase may be a polymorphonuclear granulocyte reaction. (ii) Immunofluorescence microscopy: Monoclonal staining of casts for either kappa or lambda light chains confirm the diagnosis, but clonal staining may be absent in some cases. Staining of formalin-fixed paraffin-embedded material after pronase digestion may unmask clonal staining in some of these cases. (iii) Electron microscopy: Glomeruli are unremarkable, and casts show granular electron-dense material. Crystalline substructure may be seen within these light chain casts. In rare cases, deposits of amyloid may form on the surface of the casts.