What is the clinical utility of serum protein electrophoresis (SPEP) in monoclonal gammopathies?

• A. Detects M-protein; followed by immunofixation to identify monoclonal antibody type and guide diagnosis
• B. Measures serum calcium
• C. Screens for autoimmune antibodies
• D. Detects viral antibodies

Answer: (A)

SPEP detects a monoclonal protein, the M-protein, produced by a single clone of plasma cells. When a sharp M-spike appears on the electrophoresis, immunofixation is then used to identify the exact type of monoclonal antibody (the heavy chain class and the light chain type). This combination is essential to confirm a monoclonal gammopathy and to distinguish among conditions such as multiple myeloma, MGUS, or lymphoplasmacytic disorders. It also provides a basis for monitoring disease burden over time as treatment affects the M-protein level. Other options don’t reflect what SPEP does: measuring serum calcium, screening for autoimmune antibodies, or detecting viral antibodies are different tests not assessing monoclonal proteins.