Serum protein electrophoresis (SPEP)

Serum protein electrophoresis (SPEP) is a blood test that separates the proteins in serum into distinct fractions based on their electrical charge and size. The result is reported as a tracing with six regions: albumin, alpha-1 globulin, alpha-2 globulin, beta-1 globulin, beta-2 globulin, and gamma globulin. Each region reflects different protein populations with distinct clinical significance, and the pattern of changes across all fractions together provides more diagnostic information than any individual value alone.

What SPEP is used for:

• Detecting monoclonal proteins (M-spikes) — the hallmark finding in MGUS, smoldering myeloma, and multiple myeloma
• Evaluating unexplained changes in total protein or globulin levels
• Screening for polyclonal hypergammaglobulinaemia in chronic infection, autoimmune disease, or liver disease
• Interpreting individual protein fraction changes as part of inflammatory, nutritional, or immune workups
• Monitoring known plasma cell disorders over time

How individual fractions are interpreted:

Albumin is the dominant fraction and the primary marker of nutritional status and liver synthetic function. A low albumin with elevated globulins shifts the albumin-to-globulin ratio and is a key pattern in chronic disease, liver cirrhosis, and protein-losing states.

Alpha-1 globulin includes alpha-1 antitrypsin and alpha-1 acid glycoprotein. It rises during acute inflammation and may be reduced in alpha-1 antitrypsin deficiency.

Alpha-2 globulin includes haptoglobin, alpha-2 macroglobulin, and ceruloplasmin. It is one of the most reliable acute-phase reactant fractions — rising sharply during infection, tissue injury, and inflammation, and falling in hemolytic anemia as haptoglobin is consumed.

Beta-1 globulin is primarily transferrin. It rises in iron deficiency as transferrin production increases, and falls in protein-losing conditions or inflammation.

Beta-2 globulin includes beta-lipoproteins and other proteins migrating in the beta-2 zone. Mild elevation is most commonly a non-specific inflammatory or lipoprotein-related finding. A monoclonal IgA can migrate in the beta region and may be identified as an M-spike or abnormal protein band.

Gamma globulin contains immunoglobulins (IgG, IgA, IgM). A broad polyclonal elevation reflects chronic infection or autoimmune disease. A sharp narrow spike (M-spike) indicates clonal immunoglobulin production and requires evaluation for plasma cell or lymphoid disorder. Low gamma suggests immunodeficiency.

Common SPEP patterns:

• Acute inflammation — low albumin, high alpha-2, variable beta; gamma normal
• Chronic inflammation or autoimmune — low albumin, elevated polyclonal gamma
• Iron deficiency — elevated beta-1 (transferrin)
• Liver cirrhosis — low albumin, beta-gamma bridging, polyclonal gamma
• Monoclonal gammopathy — M-spike in gamma or beta region; may have suppressed other fractions
• Nephrotic syndrome — low albumin, high alpha-2, low gamma

Related tests: SPEP findings typically prompt follow-up with serum immunofixation electrophoresis (IFE) to characterise immunoglobulin class and light chain type, serum free light chain assay, and urine protein electrophoresis (UPEP) to detect Bence Jones protein.