Short answer
Serum protein electrophoresis, often called SPEP, separates proteins in the blood into fractions so clinicians can see whether the pattern looks normal, inflammatory, or monoclonal. It can be part of a workup for MGUS, multiple myeloma, kidney disease, high total protein, anemia, bone pain, neuropathy, or a suspicious globulin pattern. SPEP is a pattern test, not a diagnosis by itself.
What the pattern may show
| Pattern | What it can mean | What usually follows |
|---|---|---|
| Narrow M-spike | Possible monoclonal protein | Immunofixation and free light chains |
| Broad gamma increase | Often polyclonal or inflammatory | Look for liver, autoimmune, or infection context |
| Low albumin or mixed fraction shifts | Can fit kidney, liver, nutrition, or protein loss patterns | Interpret with total protein, globulin, and symptoms |
| Small or unclear band | May still matter, especially if symptoms are present | IFE, urine testing, and repeat testing |
What IFE and free light chains add
Immunofixation helps identify the exact protein type when SPEP suggests something monoclonal or ambiguous. Free light chains add kappa and lambda context and can help detect light-chain disease, but kidney function can affect interpretation. A globulin test or total protein / A/G ratio may prompt SPEP, but SPEP is the follow-up pattern test that gives more detail.
When follow-up matters
MGUS is a precursor condition that does not always need immediate treatment, but it does need careful interpretation and follow-up. Multiple myeloma is a plasma-cell cancer, and symptoms such as bone pain, anemia, high calcium, kidney injury, or frequent infections raise the stakes. The result becomes more meaningful when combined with CBC, calcium, creatinine or eGFR, urine testing, symptoms, and prior protein results.
Questions to ask
- Was the pattern monoclonal, polyclonal, or not clearly abnormal?
- Was immunofixation, free light chains, or urine testing ordered?
- Do CBC, calcium, creatinine or eGFR, and symptoms suggest organ involvement?
- Is this a one-time pattern to repeat or a finding that needs hematology follow-up now?
- Could kidney disease, liver disease, inflammation, or dehydration explain part of the pattern?
What follow-up may include
- Immunofixation and serum free light chains when an M-spike or faint band needs clarification.
- CBC, calcium, creatinine or eGFR, and urine protein testing to look for organ involvement.
- Repeat SPEP when the pattern may be transient or when the first result was borderline.
- Hematology review when the protein pattern is monoclonal or symptoms raise concern.
- Kidney, liver, and inflammatory context review when the pattern is more polyclonal than monoclonal.
FAQ
What does SPEP measure?
SPEP separates serum proteins into fractions so clinicians can see whether the pattern looks normal, inflammatory, or monoclonal.
What is an M-spike?
An M-spike is a narrow peak that can suggest a monoclonal protein, which is why follow-up testing is often needed.
Does SPEP diagnose myeloma?
No. SPEP can raise concern for a plasma-cell disorder, but diagnosis depends on the full pattern, symptoms, and additional tests.
Why are immunofixation and free light chains ordered?
They help identify the protein type and can catch patterns that SPEP alone may miss, especially light-chain disease.
Can inflammation change the pattern?
Yes. Polyclonal or inflammatory changes can alter the globulin fractions without meaning a monoclonal process is present.
What usually comes next if the result is abnormal?
Common follow-up includes immunofixation, serum free light chains, CBC, calcium, creatinine or eGFR, urine testing, and sometimes hematology review.
Related guides: total protein, globulin, and A/G ratio interpretation, rouleaux on blood smear interpretation, plasma cells on CBC differential interpretation, and kidney function tests.