Serum protein electrophoresis, often shortened to SPEP or serum electrophoresis, is a blood test that separates proteins in the liquid part of blood into groups or bands. Instead of giving only one total protein number, it shows a pattern of protein fractions.
This test is often used when healthcare professionals need to look more closely at blood protein patterns, especially albumin and globulin-related patterns. MedlinePlus explains that albumin and globulin are the two major types of protein in blood: albumin makes up most blood protein, while globulins include proteins involved in infection defence and nutrient transport.
The key point is this: SPEP is not a diagnosis by itself. It is a pattern test. It can show whether protein fractions look unusual, but the reason for the pattern depends on symptoms, medical history, other blood tests, urine tests, immunoglobulin testing, and sometimes specialist review.
What is serum?
Serum is the liquid part of blood after the blood has clotted and the cells have been removed. It contains proteins, antibodies, electrolytes, hormones, nutrients, waste products, and many other substances.
SPEP uses serum because the aim is to examine proteins dissolved in the blood fluid, not the blood cells.
What does electrophoresis mean?
Electrophoresis is a laboratory technique that separates molecules based on how they move in an electric field. Different proteins have different sizes, charges, and movement patterns. When an electric current is applied, serum proteins separate into bands or zones.
In plain English: electrophoresis spreads the proteins out so the lab can see the pattern more clearly.
What proteins does SPEP look at?
SPEP commonly separates serum proteins into broad regions such as:
- Albumin
- Alpha-1 globulins
- Alpha-2 globulins
- Beta globulins
- Gamma globulins
Albumin is usually the largest single protein fraction in serum. Globulins include many different proteins, including immunoglobulins, which are antibodies made by the immune system.
Cleveland Clinic explains that serum protein electrophoresis measures gamma globulins and other trace proteins in blood serum, and that gamma globulins, also called immunoglobulins, help the immune system fight foreign substances and infections.
Why is SPEP ordered?
SPEP may be ordered when total protein, globulin, albumin/globulin ratio, symptoms, or other results suggest that protein patterns need a closer look.
Possible reasons include:
- High total protein
- High globulin
- Low albumin/globulin ratio
- Unexplained inflammation pattern
- Immune-system-related conditions
- Suspected abnormal immunoglobulin pattern
- Monitoring known protein abnormalities
- Investigation of unexplained anaemia, kidney findings, bone pain, or calcium abnormalities in selected contexts
- Follow-up of abnormal protein results
Cleveland Clinic notes that serum protein electrophoresis may be used in workups involving immune-system-related conditions such as autoimmune disease, multiple myeloma, and Waldenström’s macroglobulinemia.
SPEP vs total protein test
A total protein test measures the total amount of protein in the blood. It may also report albumin, globulin, and the albumin/globulin ratio.
SPEP goes further by separating protein fractions into a visual or numerical pattern.
MedlinePlus explains that a total protein and A/G ratio test measures total protein and compares albumin with globulin, and that the globulins test is called serum electrophoresis, which measures the levels of four different types of globulins.
So:
- Total protein tells you the overall amount.
- Albumin/globulin ratio compares two broad protein groups.
- SPEP separates protein fractions into a more detailed pattern.
What is an M protein or monoclonal band?
In some SPEP reports, the lab may describe a monoclonal band, paraprotein, M protein, or M spike. This means there may be a narrow band of immunoglobulin produced by a group of similar plasma cells.
A monoclonal band does not automatically mean cancer. It can be seen in different clinical contexts and usually needs further interpretation with tests such as immunofixation, immunoglobulin levels, serum free light chains, urine studies, full blood count, calcium, kidney markers, and clinical review.
What can abnormal SPEP patterns suggest?
Abnormal SPEP patterns may suggest that one or more protein groups are increased, decreased, or unusually shaped. Possible pattern-related questions include:
- Is albumin low?
- Are alpha proteins increased, suggesting inflammation or acute phase response?
- Are beta fractions changed?
- Are gamma globulins broadly increased?
- Is there a narrow monoclonal band?
- Is the pattern stable or changing over time?
- Are other tests abnormal?
MedlinePlus notes that high total protein may be linked with infection or multiple myeloma, while low total protein may be linked with liver disease, kidney disease, malnutrition, or malabsorption.
Polyclonal vs monoclonal pattern
A useful educational distinction is polyclonal versus monoclonal.
A polyclonal increase means many different immunoglobulin types are increased. This may occur with inflammation, infection, liver disease, autoimmune activity, or immune stimulation.
A monoclonal pattern means a narrower band is present, suggesting one dominant immunoglobulin type. This may require further testing to identify the immunoglobulin type and clinical significance.
This is where SPEP becomes a pattern-recognition test rather than a simple high/low test.
What happens during the test?
SPEP is a blood test. A healthcare professional collects blood from a vein in the arm. The laboratory separates serum proteins using electrophoresis and reports the pattern.
Preparation depends on local policy and any other tests being done at the same time. Patients should follow the instructions given by their healthcare provider or laboratory.
What tests may be ordered with SPEP?
SPEP is often interpreted with other tests, such as:
- Total protein
- Albumin
- Globulin and A/G ratio
- Full blood count
- Kidney function tests
- Calcium
- Immunoglobulin levels
- Serum free light chains
- Immunofixation
- Urine protein electrophoresis
- CRP or ESR
- Liver function tests
Key takeaway
Serum protein electrophoresis is a blood test that separates serum proteins into bands or fractions. It helps show albumin and globulin patterns more clearly than a total protein result alone.
It may be used when protein levels, globulin levels, A/G ratio, symptoms, or other results suggest the protein pattern needs closer review. Abnormal patterns can have many causes, including inflammation, infection, immune activity, liver or kidney-related issues, or monoclonal protein patterns.
The safest way to understand SPEP is: SPEP does not give one simple high/low answer; it shows a protein pattern that needs clinical interpretation.
FAQ
What does serum protein electrophoresis show?
It separates serum proteins into fractions such as albumin and globulin regions, including gamma globulins.
Is SPEP the same as total protein?
No. Total protein measures the overall amount of protein. SPEP separates proteins into bands or fractions so the pattern can be assessed.
Does an abnormal SPEP mean multiple myeloma?
Not necessarily. SPEP can be used in multiple myeloma workups, but abnormal protein patterns can have many causes and need further testing and clinical context.
What is the gamma region?
The gamma region contains many immunoglobulins, also called antibodies, which help the immune system fight infections.
Educational only. This article does not provide medical advice, diagnosis, treatment guidance, or personal result interpretation.