Serum Protein Electrophoresis (SPEP): Reading Your Profile

Serum protein electrophoresis (SPEP) is a blood test that separates the proteins in your serum into several fractions — albumin, alpha-1, alpha-2, beta, and gamma — to draw a profile. It doesn't report a single number; it produces a picture of your proteins, and its most valuable job is spotting a monoclonal gammopathy — an abnormal, narrow "spike." This guide explains what SPEP measures, what a monoclonal (M) spike is, the normal ranges for each fraction, and how to read a profile — without panic, because a spike is not the same as cancer. SPEP complements your liver function tests and is read alongside your total protein and albumin.

Key takeaways

• SPEP separates serum proteins into 5 fractions (albumin, alpha-1, alpha-2, beta, gamma) and gives a profile, not a single value.¹²
• Its main use is to detect and monitor a monoclonal gammopathy — a narrow spike in the gamma zone (an M-spike, or paraprotein) — which points toward multiple myeloma, MGUS, or Waldenström macroglobulinemia.³⁴
• A spike is almost always followed up with immunofixation, serum free light chain testing, and a urine check for Bence-Jones protein (UPEP).³⁵
• Other patterns matter too: polyclonal hypergammaglobulinemia (infection, inflammation, cirrhosis = beta-gamma bridging), hypogammaglobulinemia (immune deficiency), a nephrotic pattern (low albumin, high alpha-2), or alpha-1-antitrypsin deficiency.⁶¹
• No fasting is needed in most cases — just follow the instructions on your order.²
• A spike is not always cancer: MGUS is common after age 50 and often harmless; it's the full work-up, done by a specialist, that decides.⁷⁸

What is serum protein electrophoresis?

Your blood carries hundreds of different proteins. Electrophoresis is a lab technique that makes them migrate in an electric field: depending on their charge and size, they cluster into bands. The result is a curve with five major fractions, fastest to slowest:¹²

• albumin, by far the most abundant (the large peak on the left);
• alpha-1 globulins (including alpha-1-antitrypsin);
• alpha-2 globulins (haptoglobin, alpha-2-macroglobulin);
• beta globulins (transferrin, part of complement);
• gamma globulins — the immunoglobulins (antibodies).

The point of SPEP is not to "weigh" each protein but to reveal the shape of the curve. A bump, a dip, or — above all — a narrow, sharp spike in one fraction each tells a different story. That's why it's called a protein profile.

SPEP, immunofixation, free light chains — three complementary tests. SPEP flags an abnormality; immunofixation (IFE) identifies it (naming the immunoglobulin type, e.g. IgG kappa); serum free light chains quantify it precisely. They are usually ordered together.³⁵

Why the test is done

Clinicians order SPEP mainly to look for or monitor a monoclonal gammopathy — the abnormal production, by a clone of plasma cells, of a single identical immunoglobulin, the paraprotein. Common triggers include:³⁴⁶

• an unexplained high ESR, anemia, bone pain, kidney injury, or high calcium — the "CRAB" features of multiple myeloma;
• an abnormally high total protein, which prompts a closer look at the gamma fraction;
• suspected chronic infection, inflammatory disease, or liver disease (SPEP then complements the liver function tests);
• recurrent infections raising concern for an immune deficiency (low gamma);
• follow-up of a known gammopathy (MGUS, treated myeloma), tracking the spike over time.⁷

SPEP is a powerful screening and triage test: it doesn't diagnose on its own, but it launches the right cascade of follow-up tests.

Do you need to fast?

In general, SPEP does not require fasting — it's a routine venous blood draw. A recent meal may slightly cloud the serum (a milky look after very fatty food) but doesn't change how the fractions are interpreted. Follow the exact instructions on your order: if other tests are drawn at the same time (glucose, lipid panel), it may be those tests that require fasting (see Do you need to fast before a blood test?).²

Normal ranges

Below are indicative adult reference values, given as an absolute amount (g/L in SI units, with the common g/dL) and as a percentage of total protein. They vary by lab, technique, and age — always compare against the range printed on your report.

Note: these cutoffs are approximate and vary between labs. On a profile, the shape of the curve — a spike, a bridge, a dip — often matters more than the exact value of any one fraction. Only your clinician can interpret the tracing in your context.¹⁶

Understanding your results

A profile is read fraction by fraction, but above all as a whole. Here are the main patterns.

A spike in the gamma zone (monoclonal spike)

The result that worries people most is the monoclonal spike: a narrow, sharp band, most often in the gamma zone, reflecting the secretion of one single immunoglobulin by a plasma-cell clone. It is the signature of a monoclonal gammopathy.⁴³ The main causes:

• MGUS (monoclonal gammopathy of undetermined significance): by far the most common, especially after 50, with no active disease — just a spike to monitor;⁷⁸
• multiple myeloma: a malignant plasma-cell proliferation, often with a larger spike, anemia, bone lesions, kidney injury, or high calcium;³
• Waldenström macroglobulinemia, tied to an IgM spike;
• less often, AL amyloidosis and other lymphoid disorders.

When there's a spike, the path is clear: specialist (hematology) referral. Immunofixation names the type (IgG, IgA, IgM, kappa or lambda), serum free light chains and the kappa/lambda ratio refine the picture, and a Bence-Jones protein check is done in the urine (urine protein electrophoresis, UPEP).³⁵ It is this whole set — not SPEP alone — that separates a benign MGUS from myeloma.

MGUS is not myeloma. This is the point that keeps things in perspective: MGUS affects about 3% of people over 50 and turns into active disease only at a low rate, on the order of 1% per year. The large majority of people with a small spike will never develop myeloma; they are simply monitored.⁷⁸

Diffusely high gamma (polyclonal hypergammaglobulinemia)

When the gamma fraction is broadly raised but wide, with no spike, that's polyclonal hypergammaglobulinemia. It is reassuring in the sense that it reflects a normal immune reaction, not a clone: chronic infections, inflammatory or autoimmune disease, and especially liver disease. In cirrhosis, the beta and gamma fractions fuse into a characteristic beta-gamma bridge — one reason to read SPEP alongside your liver function tests and ESR.¹⁶

Low gamma (hypogammaglobulinemia)

A low gamma fraction signals a lack of antibodies: immune deficiency (primary or acquired), protein loss, some treatments, or — importantly — certain gammopathies in which the clone "crowds out" normal immunoglobulins. With recurrent infections, this pattern warrants an immune work-up.⁶

Abnormalities in the other fractions

• Low albumin + high alpha-2: suggests a nephrotic pattern (albumin leaking into the urine), to link with your albumin result and urine protein.¹
• Flat alpha-1: can reveal alpha-1-antitrypsin deficiency, an inherited cause of emphysema and liver disease.¹
• High alpha-1 and alpha-2: an inflammatory pattern (acute-phase proteins), to compare with CRP and the ESR.

SPEP and cancer — the nuance. A monoclonal spike is not a "cancer marker" in the usual sense. It reflects a plasma-cell clone that, most often (MGUS), stays harmless. SPEP does not screen for solid tumors; it explores proteins and plasma-cell disorders.

What affects your SPEP

Several things shift the tracing: age (gamma rises slightly over the years), pregnancy and estrogens (which alter some fractions), dehydration (which concentrates proteins), malnutrition or liver disease (low albumin), acute inflammation, and medications — especially therapeutic monoclonal antibodies such as daratumumab (an anti-CD38 antibody used in myeloma), which can appear as a small spike on SPEP and immunofixation and be mistaken for the patient's own paraprotein.⁹¹⁰ Always share your medications and context: they change the reading.

Recent research

According to recent PubMed-indexed publications:

• Free light chains and the kappa/lambda ratio have become an essential companion to SPEP. Measuring serum free light chains markedly increases the sensitivity of gammopathy screening (especially "light-chain" myelomas) and supports prognosis and monitoring; guidelines urge pairing SPEP with free light chains rather than relying on electrophoresis alone. A 2026 U.S. primary-care survey found that only a minority of clinicians follow this guideline-recommended paired testing.⁷⁵ (Yagnik B et al., J Appl Lab Med, 2026 — DOI.)
• The IMWG criteria modernized how myeloma is defined. Since 2014, the International Myeloma Working Group has added biomarkers (including a highly skewed free light chain ratio) alongside the "CRAB" organ features to diagnose myeloma earlier — directly shaping how SPEP and its companion tests are used.⁴ (Rajkumar SV et al., Lancet Oncol, 2014 — DOI.)
• Mass spectrometry is beginning to replace immunofixation in some labs. More sensitive, it detects tiny spikes, distinguishes the patient's paraprotein from therapeutic antibodies (daratumumab), and may eventually supersede electrophoretic methods for diagnosing and monitoring myeloma, according to a dedicated IMWG report.¹⁰¹¹

These findings concern diagnosis and research; they do not authorize self-medication and do not replace your physician's advice.

Get your protein electrophoresis interpreted by AI DiagMe

A protein electrophoresis is never read alone: its meaning depends on the shape of the profile, your total protein, your albumin, your liver function tests, your ESR, and your whole context. That cross-reading is what gives the result its real value.

👉 AI DiagMe interprets your lab results — blood, urine, or stool — in plain language, taking your whole profile into account. An informational service that does not provide a diagnosis and complements, never replaces, your physician.

Frequently asked questions

The bottom line

Serum protein electrophoresis (SPEP) separates your proteins into five fractions and gives a profile, not a single number. Its big role is to spot a monoclonal gammopathy — a narrow spike in the gamma zone — that points toward MGUS, multiple myeloma, or Waldenström macroglobulinemia, and that calls for a specialist, backed by immunofixation, serum free light chains, and a urine Bence-Jones check. Keep in mind that other patterns speak too (high or low gamma, a nephrotic profile, alpha-1-antitrypsin deficiency), that no fasting is needed, that ranges vary by lab, and above all that a spike is not the same as cancer — MGUS is common and often benign. No profile is read alone: it's your whole set of markers and your context that counts, which is what AI DiagMe provides, alongside your physician.

Sources

Official U.S. sources and peer-reviewed publications (PubMed, ChEMBL) used for this guide: