A 67-year-old man presents with progressive fatigue, bone pa…
A 67-year-old man presents with progressive fatigue, bone pain in his lower back, and unintentional weight loss. Laboratory results show:TestResultReference RangeCalcium11.8 mg/dL8.5–10.5 mg/dLCreatinine2.0 mg/dL0.6–1.2 mg/dLHemoglobin9.2 g/dL13.5–17.5 g/dLTotal protein9.5 g/dL6.0–8.3 g/dLPeripheral smear shows rouleaux formation, and serum protein electrophoresis reveals an M-protein spike.Which finding best confirms the underlying diagnosis and guides initial management?