A monoclonal spike on serum protein electrophoresis can be seen in which disorders?

• A. Monoclonal gammopathy such as MGUS or multiple myeloma.
• B. Acute bacterial infection.
• C. Severe anemia.
• D. Hypothyroidism.

Answer: (A)

A monoclonal spike on serum protein electrophoresis reflects a clonal expansion of plasma cells producing a single type of immunoglobulin. This sharp, defined spike is the hallmark of monoclonal gammopathies, such as MGUS or multiple myeloma, where one clone dominates immunoglobulin production. In these conditions you’re seeing a discrete band because one immunoglobulin type is overproduced by a single clone.

In contrast, acute bacterial infections trigger polyclonal activation of B cells, raising many different antibodies and producing a broad, diffuse increase in the gamma region rather than a single sharp spike. Severe anemia and hypothyroidism do not cause a monoclonal plasma cell proliferation, so they typically don’t produce a monoclonal band on SPEP; any changes are non-specific. For characterization and confirmation, immunofixation and free light-chain assays are used to identify and type the monoclonal protein.