A 70-year-old man presents with lytic bone lesions, serum protein electrophoresis showing an M-spike of 3.8 g/dL (IgG kappa), hemoglobin 8 g/dL, serum calcium 11.2 mg/dL, and creatinine 2.1 mg/dL. Bone marrow shows 35% plasma cells. Using the ISS staging system, which parameter combination defines Stage III?

• A Beta-2 microglobulin >5.5 mg/L and albumin <3.5 g/dL
• B LDH elevated plus high-risk cytogenetics
• C M-protein >3 g/dL plus lytic lesions
• D Beta-2 microglobulin ≥5.5 mg/L ✓

Explanation

The International Staging System (ISS) for multiple myeloma uses serum beta-2 microglobulin and albumin: Stage I = beta-2M <3.5 mg/L and albumin ≥3.5 g/dL; Stage II = neither I nor III; Stage III = beta-2M ≥5.5 mg/L. The Revised ISS (R-ISS) adds LDH and high-risk cytogenetics on top of ISS, but ISS Stage III is defined by beta-2M ≥5.5 mg/L alone. M-protein levels and lytic lesions are not part of ISS.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.