Understand polyclonal, monoclonal and restricted patterns on a dog or cat’s protein electrophoresis report, what immunofixation adds, and what to ask your vet.

If your dog's or cat's report says monoclonal gammopathy, the immediate question is usually whether that means cancer. It means the result deserves investigation. It does not supply a final diagnosis. The words describe how proteins separate in a laboratory test; the veterinarian must connect that finding with the examination, other test results and, when indicated, evidence from cells or tissue.

SPE is often requested after a blood chemistry panel shows increased globulins. Its useful contribution is to characterize that increase. Keep three items distinct when reading the result: the reported pattern, any immunofixation findings, and the working diagnosis recorded by the treating veterinarian.

What the report measures

Electrophoresis separates proteins according to their physical characteristics, including size and charge. The report groups them into albumin and alpha, beta and gamma globulin fractions. Some laboratories subdivide the alpha and beta groups. It combines the tracing with concentrations and an interpretation; the graph is only one part of the result. Cornell AHDC testing guidance.

Albumin normally forms a prominent narrow peak and supplies a comparison for the width of a suspicious globulin peak. Alpha fractions contain acute-phase proteins that can increase during inflammation. Beta fractions contain several types of protein, including some immunoglobulins, and gamma globulins are largely immunoglobulins. These are antibodies made by B lymphocytes and plasma cells. An antibody-related increase can therefore appear in the beta region as well as the gamma region.

The area beneath a fraction of the tracing contributes to its percentage of total protein. That percentage is combined with total protein to obtain an absolute concentration. Peak height alone is not an antibody measurement or a measure of cancer severity. Read the units and the laboratory reference interval alongside the visual pattern, and ask which fraction is actually increased.

Both agarose gel and capillary methods are used in veterinary laboratories. They can give different peak heights and fraction boundaries, so a graph from another laboratory is a poor template for diagnosing your pet. This is also why the same method matters when comparing serial results. Cornell eClinPath method and interpretation reference.

Reading polyclonal, monoclonal and restricted patterns

The shape helps the pathologist decide whether many different antibodies are contributing or whether a more restricted protein population needs clarification. Pattern terms express evidence about the protein response. They do not name its cause. The following descriptions help you understand the wording of a report, rather than classify an unlabeled graph yourself.

Report wording	What it suggests	What remains unresolved
Polyclonal gammopathy	A broad increase, usually across gamma and sometimes beta, reflects production of different antibodies.	The source of immune stimulation; the pattern is not specific to an infection or organ.
Monoclonal or monoclonal-like spike	A narrow beta or gamma band, often comparable in width to albumin, raises concern for a restricted immunoglobulin.	Whether the peak is an M-protein and whether a tumor is present. Immunofixation can clarify the protein.
Restricted oligoclonal pattern	A narrow peak on a broad base, or several restrictions, can accompany a focused immune response.	Inflammation and a concurrent neoplasm can overlap. The broad background does not settle the cause.
Split peaks	Two narrow peaks may reflect different forms of one protein, including dimerized IgA.	Two peaks do not automatically mean two tumors or two independent clones.
Acute-phase response	Increased alpha fractions, sometimes with lower albumin, support an inflammatory response.	The stimulus is not identified by the pattern, and absence of this pattern does not exclude inflammation.

Cornell describes restricted oligoclonal patterns in inflammatory and infectious conditions, including severe lymphoplasmacytic stomatitis and canine Ehrlichia canis infection. It also cautions that a similar tracing can occur with lymphoid neoplasia and concurrent antigenic stimulation. That overlap is why the report needs an interpretive comment. Cornell AHDC pattern examples.

What a polyclonal pattern usually means

A polyclonal increase commonly reflects sustained immune stimulation. Veterinary examples include chronic infections, skin disease, liver or gastrointestinal inflammation, and immune-mediated disease. Merck also lists neoplasia among possible associations. A broad pattern can direct attention toward inflammation without clearing the animal of cancer. Merck Veterinary Manual: Gammopathies in Animals.

The practical question is whether an identified condition explains the degree and persistence of the protein change. A dog with an infection still needs a plan for unexplained findings. A cat with a broad gamma increase still needs a diagnosis based on its own clinical picture. The curve cannot distinguish among all the conditions that stimulate antibody production.

Feline infectious peritonitis (FIP) can produce an acute-phase response plus a polyclonal gammopathy. Cornell describes paired serum and abdominal-fluid electrophoresis as supportive evidence in cats with effusion. Similar protein changes occur in other inflammatory conditions, so matching serum and fluid patterns do not confirm FIP. The feline referral study likewise found that polyclonal changes were not specific for FIP. Cornell guidance on serum and body-fluid testing.

Why a narrow spike raises concern

An M-protein is an immunoglobulin associated with a restricted cell population. Plasma cell tumors, including multiple myeloma and extramedullary plasmacytoma, and some B-cell tumors, including lymphoma and chronic lymphocytic leukemia, can produce these proteins. A narrow spike is consequently an important finding to investigate, rather than dismiss as an incidental abnormality.

Immunoglobulin classes provide context rather than a tumor label. Myeloma proteins in dogs are commonly IgG or IgA; in cats they are usually IgG. These tendencies do not make a particular class diagnostic, and canine expectations should not be applied as a fixed rule to cats. Merck Veterinary Manual species distinctions.

Infectious and inflammatory responses can look monoclonal on SPE, and monoclonal gammopathy of undetermined significance (MGUS) has been suggested in dogs. MGUS is not an assurance that a finding is harmless or will never progress. It is a possible explanation after clinical investigation, not a conclusion an owner can draw from a small peak. Human progression percentages do not supply a prognosis for a dog or cat.

What the two veterinary studies actually show

The 155-cat referral series

Taylor and colleagues retrospectively examined 155 feline SPE results from the University of Bristol Feline Centre. Among 81 cats with increased gamma globulins, 77 (95.1%) had a polyclonal pattern. Four cats had patterns described as monoclonal: one with confirmed FIP, one with lymphoma, and two with splenic plasmacytoma, of which one was confirmed and one suspected. Taylor et al., Journal of Feline Medicine and Surgery, 2010.

The important distinction is between an observed narrow pattern and proof of an antibody clone. The investigators did not perform immunoelectrophoresis to confirm the immunoglobulin subtype and monoclonal nature of those peaks. The FIP cat had a spike within a broad polyclonal elevation. Describing all four as confirmed monoclonal proteins would make the study appear more definitive than it was.

These were selected referral cases from 2002–2009, and 136 of 155 had an abnormal SPE result. The retrospective assessments, clinical selection and incomplete histologic confirmation of FIP limit generalization. The figures show that broad increases predominated in this study and that narrow patterns had more than one explanation. They do not mean that a newly tested cat has a 95.1% chance of a benign condition. Polyclonal is a pattern category, not a prognosis.

The 112-dog immunofixation group

Jornet-Rius and colleagues evaluated 143 archived serum samples from dogs seropositive for vector-borne pathogens. Immunofixation was performed in 112 with abnormal globulin findings and adequate sample volume. Of these, 84 (75%) had polyclonal expansions, including 38 restricted polyclonal patterns. Only two had combined SPE and immunofixation findings suggestive of an M-protein. Jornet-Rius et al., Veterinary Clinical Pathology, 2024.

The two cases illustrate why follow-up matters. An Ehrlichia canis-seropositive dog had IgA restrictions and undiagnosed splenic lesions; active infection and concurrent neoplasia were not resolved. A heartworm-seropositive dog had a low-concentration IgG restriction and three years of follow-up without evidence of systemic disease, including normal globulins on repeat chemistry. Neither observation establishes that a positive pathogen test caused the restricted protein.

Another heartworm-seropositive sample had a beta-1 peak that could have looked monoclonal on SPE alone. Immunofixation showed diffuse IgG4 labeling, making it inconsistent with an M-protein. The study therefore supports examining the protein with an additional method rather than relying on peak shape. It does not show that all spikes in exposed dogs are infectious or harmless.

Seropositivity can reflect previous exposure, medical records were often unavailable, and immunoglobulin-secreting neoplasia was not rigorously excluded across the group. These were archived samples, not a population survey of all dogs with spikes. The feline and canine studies used different enrollment and testing methods; combining their counts into a single cancer-risk estimate would be misleading.

What immunofixation adds—and what it cannot settle

Immunofixation uses antibodies to identify immunoglobulin heavy and light chains after electrophoretic separation. Depending on the assay, it can characterize the involved class and reveal a restricted protein hidden within a broad background. Cornell identifies it as the preferred method for confirming immunoglobulin type and for detecting urinary Bence Jones protein, or free light chains. Cornell eClinPath immunofixation guidance.

Ask whether immunofixation was actually performed, what specimen was tested, and what the interpretation concluded. A statement such as suggestive of an M-protein is different from a tissue diagnosis of multiple myeloma. Identifying a restricted immunoglobulin supplies another piece of evidence; it does not locate the abnormal cells or establish their behavior. Serum testing and urine light-chain testing also answer different questions.

The 2024 paper cites an earlier canine study in which combined SPE and immunofixation criteria had estimated sensitivity of 95.1% and specificity of 81.4% for M-protein detection. Those are study performance estimates for specified criteria, not a 95.1% probability that an individual pet has cancer. The earlier study included relatively few infectious cases, which was part of the reason for examining vector-borne-seropositive dogs separately.

Background immunoglobulin concentrations can also help interpretation. Cornell notes that uninvolved classes are often decreased with antibody-producing neoplasms, while they may be preserved with infectious responses. Its 2018 bulletin describes radial immunodiffusion (RID) for canine IgG, IgM and IgA, and feline IgG. RID quantifies a class rather than establishing clonality and should never be used alone to identify lymphoid neoplasia. Availability should be confirmed with the laboratory. Cornell AHDC bulletin on immunoglobulin measurement.

Sample and method checks before interpreting a spike

Serum is preferred because clotting removes fibrinogen. In plasma, fibrinogen can create a beta-region peak that complicates interpretation. That is a reason to check specimen type with the laboratory, rather than assume that every narrow peak represents an abnormal antibody. A suspected artifact is an interpretive question, not permission to ignore the report.

Laboratory acceptance policies vary. As checked on October 16, 2026, TVMDL test 1204 lists 0.5 mL of serum or lithium heparin plasma. It asks submitters to avoid hemolysis and separate the sample from red cells into an additive-free transport tube. The listing describes gel electrophoresis and pathologist interpretation when indicated. This is one laboratory example, not a universal collection rule or a promise about a clinic’s charge or turnaround. TVMDL Protein Electrophoresis test listing.

Hemolysis can introduce hemoglobin-haptoglobin complexes, which typically migrate in the beta-2 region in dogs and cats. Cornell’s guidance and the 2024 canine paper both support checking whether a suspicious peak is an immunoglobulin or an interfering protein. Sample discoloration and laboratory comments belong in that discussion. The owner does not need to decide from the appearance of the tube.

Split peaks require a different distinction: IgA dimerization can produce two forms of one protein. That is protein behavior rather than necessarily a collection mistake. Method differences can also alter the tracing. Keep the laboratory name and method with previous results so the clinician and pathologist can make an appropriate serial comparison, especially if testing is transferred between laboratories.

How the veterinarian connects the result to a diagnosis

The workup depends on the clinical findings. A historical specialist reference by Paul Mellor, published through VIN in 2007, describes combining blood and urine testing, imaging, cell or tissue examination, and immunolabeling in suspected myeloma-related disorders. Its value here is the need for converging evidence; it should not be presented as a current universal consensus protocol or a fixed marrow-cell threshold. Mellor: Diagnosis of myeloma related disorders.

Clinical context: the veterinarian reviews the examination, symptoms and CBC/chemistry results to decide what else needs explanation. The height of the peak does not replace those findings.
Infectious evidence: testing is chosen for species, exposure, travel and signs. A positive antibody result alone does not prove active disease or explain every protein abnormality.
Protein characterization: the pathologist may recommend immunofixation or additional immunoglobulin measurements when the pattern is restricted or ambiguous.
Imaging and sampling: suspected bone, organ or lymph-node disease may lead to imaging, cytology or biopsy. Bone marrow examination is considered when the suspected disorder warrants it; it is not an automatic consequence of any spike.
Urine assessment: urine electrophoresis or immunofixation can investigate immunoglobulin light chains when relevant. This is a different question from simply quantifying total urinary protein.

For canine multiple myeloma, the historical reference describes marrow evidence together with paraproteinemia, urinary light chains or osteolytic lesions. It also emphasizes that feline myeloma-related disease can involve tissues outside the marrow. This is why a dog-derived checklist should not become a rule for excluding disease in a cat. The treating veterinarian or specialist selects and interprets the investigation.

Infection and neoplasia can coexist. Finding one plausible inflammatory source does not resolve unexplained lesions or a persistent restricted protein. Conversely, ordering oncology investigations does not mean cancer is already established. A useful discussion identifies which possibilities remain open and which next result would change the working diagnosis.

What to keep with the report and ask at follow-up

Request the complete report, including the tracing and interpretive comments, rather than retaining only a cropped image or the word monoclonal. For a follow-up discussion, a short record can connect the laboratory findings to the clinical plan without turning a pattern label into a diagnosis. The following fields are an organizational aid, not a diagnostic scoring system.

Record field	What to capture
Specimen and method	Collection date, serum or plasma, laboratory, method if stated, and sample-quality comments.
Reported pattern	The pathologist’s wording and which fractions are outside that laboratory’s intervals.
Immunofixation status	Not performed, pending, or completed; retain the interpretation and specimen type.
Working explanation	The veterinarian’s suspected or confirmed condition, with remaining uncertainty clearly recorded.
Next decision	Which investigation or recheck is planned, who will review it, and how results will be communicated.

Does the laboratory consider this a polyclonal, restricted or monoclonal-like pattern, and how certain is that classification?
Would immunofixation change interpretation in this case, or has it already been performed?
Which findings support the current explanation, and which findings remain unexplained?
What is the next decision the proposed test will help make?
If we repeat electrophoresis, how will the results be compared and when should we discuss them?

There is no single retesting interval or investigation package for every dog and cat in these sources. Agree the timing and next step with the clinician who knows the case. The goal is a report with an explained pattern, a clear account of what has and has not been established, and a plan for resolving the remaining uncertainty.

Vet Med Guide

Your Pet's Protein Electrophoresis Report: A Spike Is Not a Cancer Diagnosis