Prepared by: Omar Adwan — DHA-Licensed Medical Laboratory Technologist | Founder, MedLab Academy
Last Updated: September 20, 2026
Quick Laboratory Answer
Serum protein electrophoresis (SPEP) separates serum proteins into characteristic fractions, including albumin, alpha-1, alpha-2, beta and gamma regions. A normal SPEP pattern shows a dominant albumin peak followed by smaller globulin fractions and a relatively broad gamma region. A narrow, discrete peak or band—often called an M-spike, M-protein, monoclonal component or paraprotein—may indicate a monoclonal immunoglobulin.
An M-spike does not by itself diagnose multiple myeloma. Serum immunofixation, serum free light chains, quantitative immunoglobulins, CBC, calcium, kidney function and other clinical investigations may be required. Conversely, a normal SPEP does not completely exclude a clinically important monoclonal gammopathy, especially when the abnormal protein is small, light-chain predominant or migrates in a less obvious region.
Authoritative Information Box
Primary guidance reviewed: NICE, NCBI Bookshelf and International Myeloma Working Group literature.
Information verified: September 20, 2026
NICE — Myeloma: Diagnosis and Management | NCBI Bookshelf — Electrophoresis | IMWG — Serum Free Light Chain Guidelines
Serum protein electrophoresis is one of the most important laboratory tests for evaluating abnormal serum proteins and detecting possible monoclonal gammopathies. It may be requested when laboratory or clinical findings raise concern for a plasma-cell or lymphoplasmacytic disorder, but it is also useful for recognizing broader patterns associated with inflammation, liver disease, protein loss and immunoglobulin abnormalities.
The most recognizable abnormality on SPEP is a narrow monoclonal protein peak, commonly called an M-spike. Correct laboratory interpretation, however, requires more than simply identifying a peak. The laboratory professional should evaluate the location, shape and quantity of the abnormality, the background gamma region, total protein and albumin concentrations, other biochemical findings and, when indicated, serum immunofixation and serum free-light-chain testing.
What Is Serum Protein Electrophoresis (SPEP)?
Serum protein electrophoresis is a laboratory technique that separates serum proteins according to their physicochemical properties, particularly their migration in an electrical field. Under commonly used alkaline electrophoretic conditions, serum proteins form several recognizable zones.
- Albumin
- Alpha-1 globulins
- Alpha-2 globulins
- Beta globulins
- Gamma globulins
Some analytical systems divide the beta region into beta-1 and beta-2. Modern laboratories may use agarose gel electrophoresis or capillary electrophoresis. The resulting distribution is evaluated visually and/or by densitometric or electrophoretic tracing.
Why Is SPEP Ordered?
SPEP may be requested when a clinician or laboratory needs to investigate an abnormal protein pattern or possible monoclonal immunoglobulin.
- Unexplained high total protein or calculated globulin.
- Low albumin-to-globulin ratio.
- Unexplained anemia.
- Renal dysfunction.
- Hypercalcemia.
- Bone pain or suspicious bone lesions.
- Unexplained neuropathy.
- Recurrent infections or suspected immunoglobulin abnormalities.
- Suspected monoclonal gammopathy.
- Monitoring of a previously identified monoclonal protein.
For related background testing, see Liver Function Tests, Albumin, Total Protein & Globulin Interpretation and the Complete Blood Count (CBC) Guide .
Normal SPEP Pattern
A normal SPEP tracing has a characteristic distribution rather than one universal set of numerical percentages. The albumin fraction normally forms the largest and most prominent peak. It is followed by smaller alpha-1 and alpha-2 fractions, the beta region and a broader, less sharply defined gamma region.
| SPEP Region | Important Components | Typical Appearance |
|---|---|---|
| Albumin | Albumin | Largest, relatively sharp peak |
| Alpha-1 | Alpha-1 antitrypsin and other alpha proteins | Small fraction |
| Alpha-2 | Haptoglobin, alpha-2 macroglobulin, ceruloplasmin and others | Moderate fraction |
| Beta | Transferrin, complement components, beta lipoproteins and some immunoglobulins | One or two beta fractions depending on method |
| Gamma | Predominantly immunoglobulins | Broad heterogeneous region |
Albumin Region
Albumin usually produces the largest peak on SPEP because it is the most abundant protein in normal serum. A reduced albumin fraction may occur with reduced hepatic synthesis, renal protein loss, protein-losing gastrointestinal disorders, inflammation, malnutrition, severe illness or hemodilution.
A reduced albumin concentration should not automatically be attributed to liver disease. Kidney function and urinary protein loss may provide important complementary information. See: Urinalysis: Proteinuria, Physical, Chemical & Microscopic Examination and High Creatinine, eGFR & Kidney Function .
Alpha-1 Region
The alpha-1 fraction contains proteins including alpha-1 antitrypsin and other acute-phase proteins. An increased alpha-1 fraction may occur as part of an acute inflammatory response. A markedly reduced alpha-1 region can raise consideration of reduced alpha-1 antitrypsin, although SPEP is not a definitive diagnostic test for alpha-1 antitrypsin deficiency.
Alpha-2 Region
Major components of the alpha-2 region include haptoglobin, alpha-2 macroglobulin and ceruloplasmin. The alpha-2 fraction may increase in acute inflammatory responses and can become prominent in nephrotic protein-loss patterns because large proteins such as alpha-2 macroglobulin are relatively retained while smaller proteins are lost.
Inflammatory markers can provide useful context. See High CRP Levels: Causes & Laboratory Interpretation and Erythrocyte Sedimentation Rate (ESR): Complete Laboratory Guide .
Beta Region
The beta region contains several proteins, including transferrin, complement components and beta lipoproteins. Some immunoglobulins—particularly certain IgA monoclonal proteins—may also migrate in the beta region.
Gamma Region
The gamma region contains most circulating immunoglobulins and is especially important when evaluating possible gammopathies. Normal gamma-region proteins are produced by many different plasma-cell clones, creating a relatively broad, heterogeneous pattern.
- Monoclonal gammopathy: a narrow, discrete abnormal component.
- Polyclonal gammopathy: a broad-based increase involving multiple immunoglobulin populations.
What Is an M-Spike?
An M-spike is a discrete electrophoretic peak produced by a relatively homogeneous monoclonal immunoglobulin or immunoglobulin component. It may also be described as an M-protein, monoclonal protein, monoclonal component, paraprotein or monoclonal band.
Many M-proteins migrate in the gamma region and appear as a narrow peak contrasting with the broader normal polyclonal gamma background. However, monoclonal proteins can migrate outside the classic gamma zone, including the beta region.
Does an M-Spike Mean Multiple Myeloma?
No. Detection of an M-protein does not automatically establish a diagnosis of multiple myeloma.
Monoclonal proteins may be associated with several conditions, including:
- Monoclonal gammopathy of undetermined significance (MGUS).
- Smoldering multiple myeloma.
- Multiple myeloma.
- Waldenström macroglobulinemia.
- Other lymphoplasmacytic or plasma-cell disorders.
- AL amyloidosis and other selected monoclonal gammopathies.
The significance of an M-protein depends on the full clinical and laboratory context. Relevant investigations can include quantitative immunoglobulins, serum free light chains, CBC, calcium, kidney function and, when clinically required, bone marrow and imaging studies.
Related MedLab Academy guides: Calcium Blood Test , BUN & Kidney Function , and Low Hemoglobin & Anemia Interpretation .
Monoclonal vs Polyclonal Gammopathy
| Feature | Monoclonal | Polyclonal |
|---|---|---|
| Typical SPEP appearance | Narrow, discrete peak or restricted band | Broad-based gamma increase |
| Protein source | One dominant clone | Multiple immunoglobulin-producing clones |
| Common context | MGUS, plasma-cell or lymphoplasmacytic disorders | Chronic inflammation, infection, autoimmune or liver disease |
| Immunofixation | May identify a restricted heavy/light-chain combination | Usually demonstrates a heterogeneous immunoglobulin pattern |
Polyclonal Hypergammaglobulinemia
Polyclonal hypergammaglobulinemia produces a broad increase across the gamma region rather than a single narrow spike. It may be seen with chronic infections, chronic inflammatory disorders, autoimmune disorders, chronic liver disease and other forms of sustained immune stimulation.
A broad gamma increase should therefore not be interpreted as an M-spike solely because the gamma fraction is elevated. If autoimmune disease is part of the clinical differential, see: ANA Blood Test: Positive vs Negative, Titer & Patterns .
Acute Inflammatory SPEP Pattern
Acute inflammation can alter several electrophoretic fractions. A possible pattern may include:
- Reduced albumin.
- Increased alpha-1 proteins.
- Increased alpha-2 proteins.
- Variable changes in other fractions.
SPEP alone cannot determine the cause of inflammation. CRP and other clinical information should be interpreted alongside the electrophoretic pattern. Ferritin can also rise as an acute-phase reactant. See: High Ferritin Levels: Causes & Laboratory Interpretation .
Nephrotic Protein-Loss Pattern
Significant renal protein loss can create a recognizable electrophoretic pattern. Findings may include reduced albumin, a relatively prominent alpha-2 fraction and changes in gamma proteins. The exact pattern depends on the severity and duration of protein loss and the patient's broader clinical condition.
SPEP should not be used alone to diagnose nephrotic syndrome. Urine protein testing, albumin, kidney function and clinical findings are important for correlation.
SPEP in Liver Disease
Chronic liver disease can alter albumin and immunoglobulin distribution. Patterns may include reduced albumin with a broad polyclonal increase in gamma proteins. Some liver disorders may produce apparent blending or bridging between beta and gamma regions, but interpretation must remain method-specific and should be correlated with liver chemistry, immunoglobulins and the clinical picture.
What Is Serum Immunofixation?
Serum immunofixation electrophoresis (IFE) is a more specific technique used to characterize an abnormal immunoglobulin detected or suspected on SPEP. Whereas SPEP shows the overall distribution of serum protein fractions, immunofixation uses antisera directed against immunoglobulin heavy and light chains to determine whether a restricted monoclonal component is present and, when detectable, to identify its type.
Common heavy-chain targets include IgG, IgA and IgM, while light-chain assessment generally includes kappa and lambda. The exact panel used depends on the laboratory method and clinical requirements.
NICE recommends serum immunofixation when serum protein electrophoresis is abnormal in the investigation of possible myeloma or MGUS. Importantly, SPEP, immunofixation, serum free light chains or urine electrophoresis should not be used individually as stand-alone tests to exclude myeloma.
Serum Free Light Chains: Kappa, Lambda & Ratio
Plasma cells normally produce immunoglobulin light chains in association with heavy chains, while small quantities of free kappa and lambda light chains circulate independently. Serum free light-chain assays measure these unbound light chains and usually report:
- Free kappa concentration.
- Free lambda concentration.
- Kappa/lambda ratio.
A markedly abnormal ratio may support the presence of a clonal light-chain process, but results must be interpreted carefully. Kidney dysfunction can increase free light-chain concentrations because renal clearance is reduced, and the applicable reference interval may depend on the assay and clinical setting.
SPEP vs Immunofixation vs Free Light Chains
| Test | Main Role | Important Limitation |
|---|---|---|
| SPEP | Displays serum protein pattern and can quantify a measurable M-protein | Small or atypically migrating monoclonal proteins may be difficult to detect |
| Immunofixation | Confirms and types a suspected monoclonal immunoglobulin | Primarily qualitative; not the preferred method for routine M-protein quantification |
| Serum free light chains | Detects and monitors free kappa/lambda abnormalities | Kidney function and assay-specific factors affect interpretation |
How Is an M-Spike Quantified?
When a discrete monoclonal peak can be clearly separated from surrounding proteins, many electrophoresis systems estimate its concentration by densitometric or capillary integration and relate the measured fraction to the total serum protein concentration.
Quantification becomes more difficult when the monoclonal protein is small, overlaps another fraction, migrates in the beta region, or lies on a broad polyclonal background. The laboratory should follow validated procedures for defining integration boundaries and reporting limitations. Serial results are most useful when the same method and laboratory are used whenever possible.
Specimen Requirements & Pre-Analytical Considerations
Serum is generally preferred for routine SPEP. Plasma can produce an additional fibrinogen band or peak, typically in the beta-gamma region, which may complicate interpretation and can mimic a restricted abnormality.
Pre-Analytical Checks
- Confirm patient identification and specimen labeling.
- Use the laboratory-approved serum collection tube.
- Allow appropriate clot formation before centrifugation when required.
- Assess serum for hemolysis, lipemia or other specimen-quality concerns.
- Avoid unnecessary repeated freeze-thaw cycles.
- Follow validated storage and stability requirements for the local method.
- Review recent transfusion or immunoglobulin therapy when clinically relevant.
NCBI notes that appropriate specimen handling is important in electrophoretic testing and that repeated freezing and thawing can affect proteins and potentially alter interpretation.
Analytical Methods: Agarose Gel vs Capillary Electrophoresis
Agarose Gel Electrophoresis
Proteins migrate through a gel matrix and are visualized after staining. Densitometry can be used to quantify the relative distribution of protein fractions. Visual review remains important for identifying restricted bands or unusual patterns.
Capillary Electrophoresis
Capillary systems separate proteins in narrow capillaries and generate an electropherogram. They offer automation and high throughput, but interpretation still requires recognition of atypical migration, analytical interference and method-specific artifacts.
Laboratories should validate analytical performance, establish or verify reference intervals, maintain quality control and ensure that abnormal traces receive appropriate technical review. For broader laboratory quality principles, see: Internal Quality Control (IQC), Westgard Rules & Laboratory Quality Management .
Analytical Limitations & Potential Interferences
SPEP is powerful but not infallible. Important limitations include:
- Small monoclonal proteins: may be below the visual or quantification threshold of SPEP.
- Beta-region migration: monoclonal proteins can overlap normal beta proteins.
- Light-chain disease: SPEP can be less sensitive when the abnormal protein is predominantly free light chain.
- Polyclonal background: a broad gamma increase can obscure a small restricted component.
- Fibrinogen: plasma or incompletely clotted serum may create a band that complicates interpretation.
- Hemolysis: can alter the protein pattern and should be assessed according to local procedures.
- Therapeutic monoclonal antibodies: selected therapies may produce bands that can interfere with interpretation in some methods.
- Method differences: agarose and capillary systems may not display every abnormality identically.
Practical Laboratory Interpretation Strategy
- Check specimen suitability. Confirm that the sample is appropriate serum and review quality issues.
- Review total protein and albumin. Compare with the electrophoretic distribution.
- Examine every fraction. Do not focus only on the gamma region.
- Assess shape. A narrow restricted component differs from a broad polyclonal increase.
- Assess location. Monoclonal proteins may appear in gamma, beta or another region.
- Quantify when appropriate. Report a measurable M-protein according to the validated laboratory method.
- Correlate with immunofixation and free light chains. Especially when monoclonality is suspected.
- Review complementary tests. CBC, calcium, creatinine/eGFR, quantitative immunoglobulins and other clinically relevant studies.
- Compare with previous results. Trend assessment can be more informative than one isolated measurement.
- Escalate unusual patterns. Follow the laboratory's review and referral procedure for uncertain or clinically important findings.
Common SPEP Interpretation Errors
- Calling every elevated gamma fraction an M-spike.
- Assuming every M-spike means multiple myeloma.
- Ignoring a narrow abnormality in the beta region.
- Using SPEP alone to exclude a monoclonal gammopathy.
- Failing to correlate with immunofixation and free light chains when indicated.
- Using universal numerical SPEP fraction ranges instead of local validated intervals.
- Interpreting a plasma fibrinogen peak as a monoclonal protein.
- Ignoring renal function when interpreting serum free light chains.
- Comparing serial M-protein values obtained by different methods without considering method differences.
Practical Laboratory Cases
Case 1 — Narrow Gamma-Region Peak
A patient has elevated total protein and a narrow gamma-region spike on SPEP. Immunofixation demonstrates a restricted immunoglobulin pattern.
Laboratory interpretation: The findings support a monoclonal protein, but the electrophoretic result alone does not distinguish MGUS, smoldering myeloma, multiple myeloma or another monoclonal gammopathy. Clinical evaluation and additional laboratory investigations are required.
Case 2 — Broad Gamma Increase
SPEP demonstrates a broad-based gamma increase without a discrete narrow component. CRP is increased and the clinical history suggests chronic inflammatory disease.
Laboratory interpretation: The broad pattern is more consistent with polyclonal hypergammaglobulinemia than a classic monoclonal M-spike.
Case 3 — Renal Dysfunction with Abnormal Free Light Chains
Serum free kappa and lambda concentrations are increased in a patient with impaired kidney function. SPEP does not show a large discrete M-spike.
Laboratory interpretation: Reduced renal clearance can increase free light-chain concentrations. Interpretation should use the assay-specific approach, the kappa/lambda ratio, kidney function, immunofixation and the complete clinical picture rather than the absolute light-chain concentrations alone.
Case 4 — Rouleaux on Peripheral Smear
A CBC sample shows marked rouleaux formation on peripheral smear with an elevated ESR and high total protein. SPEP is requested and identifies an abnormal protein pattern.
Laboratory interpretation: Rouleaux can be associated with increased plasma proteins but is not specific for a monoclonal gammopathy. SPEP, immunofixation and related investigations provide more specific information.
See: Peripheral Blood Smear & RBC Morphology and LDH Blood Test: Hemolysis, Tissue Injury & Laboratory Interpretation .
When Should SPEP Be Repeated?
Repeat testing depends on the reason for testing, the initial result, clinical findings and the monitoring plan established by the treating team. A previously detected monoclonal protein may require serial measurement, while an unexpected or technically uncertain pattern may require confirmation or additional testing rather than simple repetition.
Where serial M-protein measurement is clinically required, consistency of analytical method and laboratory can improve comparability. Monitoring frequency for confirmed plasma-cell disorders should follow the treating clinician's plan and current disease-specific guidance.
Related MedLab Academy Laboratory Guides
- Complete Blood Count (CBC): Interpretation & Case Studies
- Peripheral Blood Smear: RBC Morphology & Interpretation
- High Creatinine, eGFR & Kidney Function
- BUN Blood Test & BUN/Creatinine Ratio
- Calcium Blood Test: Total, Ionized & Corrected Calcium
- High CRP Levels & Laboratory Interpretation
- ESR: Complete Laboratory Guide
- High Ferritin Levels: Causes & Interpretation
- Liver Function Tests, Albumin, Total Protein & Globulin
- Urinalysis: Proteinuria & Microscopic Examination
- LDH Blood Test: High LDH, Hemolysis & Interpretation
- ANA Blood Test: Titer, Patterns & Interpretation
- RDW Blood Test: RDW-CV, RDW-SD & MCV Interpretation
- Low Hemoglobin: CBC & Anemia Interpretation
- Internal Quality Control (IQC) & Westgard Rules
Frequently Asked Questions
What does a high M-spike mean?
A measurable M-spike indicates a restricted monoclonal protein component, but the number alone does not determine the underlying diagnosis. The result must be correlated with immunofixation, free light chains, clinical findings and other investigations.
Can SPEP be normal in multiple myeloma?
A normal SPEP does not by itself exclude myeloma or another clinically important monoclonal gammopathy. Small monoclonal proteins, light-chain abnormalities or other atypical patterns may require immunofixation, serum free light chains and additional investigation.
What is the difference between SPEP and immunofixation?
SPEP displays the overall serum protein pattern and can quantify a measurable monoclonal peak. Immunofixation is more specific for confirming and typing a monoclonal immunoglobulin.
Is a broad gamma increase the same as an M-spike?
No. A broad gamma increase is more typical of a polyclonal response, whereas a classic M-spike is narrow and restricted. Difficult or atypical patterns may require confirmatory testing.
Why should serum be used instead of plasma for SPEP?
Plasma contains fibrinogen, which can create an additional band or peak and complicate interpretation. Serum is therefore generally preferred for routine serum protein electrophoresis.
Authoritative & Scientific References
- National Institute for Health and Care Excellence (NICE). Myeloma: diagnosis and management — laboratory investigations .
- Sonagra AD, Zubair M, Dholariya SJ. Electrophoresis. StatPearls, NCBI Bookshelf .
- Dispenzieri A, Kyle R, Merlini G, et al. International Myeloma Working Group guidelines for serum-free light chain analysis .
- Dimopoulos M, Kyle R, Fermand JP, et al. Consensus recommendations for standard investigative workup in plasma cell disorders .
- Rajkumar SV, Dimopoulos MA, Palumbo A, et al. International Myeloma Working Group updated criteria for the diagnosis of multiple myeloma .
- Kumar S, Paiva B, Anderson KC, et al. IMWG consensus criteria for response and minimal residual disease assessment in multiple myeloma .
Reference note: Diagnostic criteria, monitoring recommendations, analytical methods and assay-specific interpretation may change. Readers should consult the latest official guideline, manufacturer instructions, laboratory SOPs and local clinical requirements.
Medical & Educational Disclaimer
This article is intended for education and professional development in medical laboratory science. It does not replace patient-specific medical advice, diagnosis, treatment, institutional standard operating procedures, manufacturer instructions, laboratory validation requirements or the judgment of qualified healthcare professionals. Reference intervals, analytical methods and interpretive criteria vary between laboratories and must be applied according to the performing laboratory and the patient's clinical context.