Serum Protein Electrophoresis (SPEP)

What is Serum Protein Electrophoresis (SPEP)?

Separates blood proteins into distinct bands to help evaluate protein patterns and detect abnormal protein production.

Serum protein electrophoresis (SPEP) is a laboratory technique that applies an electric current to blood serum, causing its proteins to separate into distinct bands based on size and electrical charge, primarily albumin and the alpha-1, alpha-2, beta, and gamma globulin fractions. This test relates to the immune system, liver, and kidneys, since these organs and immune cells produce or regulate most of these proteins. Clinicians commonly order SPEP to evaluate unexplained fatigue, unusual infections, bone discomfort, kidney findings, or abnormal total protein results, and it is a key tool for detecting abnormal antibody production, such as in certain plasma-cell disorders, as well as patterns associated with chronic inflammation or liver disease. Because SPEP shows an overall pattern rather than a single number, clinicians interpret the shape and relative size of each band together with other tests, such as immunofixation, to understand what a particular pattern may reflect.

Tests often checked alongside this

• Total Protein — the overall measure that SPEP breaks down into fractions
• Albumin — the single largest protein fraction, often assessed together
• Immunofixation Electrophoresis — used to further characterize any abnormal band
• Liver function tests — relevant since the liver produces most non-immunoglobulin serum proteins
• Kidney function tests — relevant since protein loss or filtering issues can shift the pattern

How this can show up in how you look and feel

• May be associated with fatigue in some individuals when patterns are notably abnormal
• May be associated with unusual or recurrent infections in certain contexts
• May be associated with unexplained bone or back discomfort in select situations
• May be associated with swelling in some cases related to protein imbalance

What can affect this marker

• Age
• Hydration status
• Inflammation
• Infection
• Lab variability between laboratories

What to track over time

• Whether the overall band pattern remains stable or shifts on repeat testing
• How SPEP findings correlate with total protein, albumin, and other targeted follow-up tests
• Repeat testing may be considered if an abnormal band is identified, to monitor for change over time

What to ask your doctor

• What does my overall SPEP pattern show, and were any bands outside the expected shape?
• Is further testing, like immunofixation, needed to clarify any band?
• How does this fit with my other liver, kidney, or immune-related results?
• Should this be repeated periodically to monitor for change?

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