Serum protein electrophoresis (SPEP)
A lab test that separates the proteins in the blood into bands to look for an abnormal 'monoclonal' spike — an M-protein. Normally there is no such spike; finding one points toward a plasma-cell disorder such as myeloma or the pre-cancerous state MGUS, and its size is measured in g/L.
What it measures
Serum protein electrophoresis spreads the proteins in the blood out into a small number of bands according to how they move in an electric field. The largest band is albumin, and the rest are the globulins, including the antibodies (immunoglobulins). In health, the antibody band is broad and smooth, because it is made by many different plasma cells producing a diverse mix of antibodies. The test's purpose is to spot the opposite: a sharp, narrow spike — a monoclonal band, or 'M-protein' — which appears when a single clone of plasma cells overproduces one identical antibody. Finding an M-protein is the classic clue to a plasma-cell disorder: multiple myeloma, the pre-cancerous condition MGUS, Waldenström's macroglobulinaemia, and light-chain amyloidosis. When a spike is seen, its type is confirmed by a follow-on test (immunofixation) and its size is quantified in g/L, which is then followed over time to monitor the condition. So SPEP is essentially a search for a monoclonal protein: normally there is none, and its presence and size carry the meaning. It also gives a general picture of the protein bands, which can be altered in inflammation, liver disease or low antibody levels.
What a high value can mean
- A monoclonal (M-protein) band — the key abnormal finding; a spike suggesting one clone of plasma cells is overproducing a single antibody.
- Multiple myeloma — a large M-protein, usually with other features (anaemia, high calcium, kidney or bone problems).
- MGUS — a small M-protein without myeloma features; common and monitored over time.
- Waldenström's macroglobulinaemia — an IgM monoclonal band.
- A broad rise in the antibody band (polyclonal) — not a clonal spike; reflects infection, inflammation or liver disease.
What a low value can mean
- No monoclonal band — the normal, reassuring result.
- A reduced antibody band — low immunoglobulins, which can predispose to infection and prompts its own work-up.
When to discuss with a doctor
Serum protein electrophoresis is usually requested when a plasma-cell disorder is suspected — for example with unexplained anaemia, a high calcium, kidney impairment, bone pain, or a raised total protein — to look for a monoclonal protein. Finding an M-protein needs interpretation: a small band may be MGUS, monitored over time, while a larger band with other features points toward myeloma and a fuller work-up. The size of the band is tracked to follow the condition and its treatment. This is specialist territory, interpreted by haematology alongside free light chains and the other markers. Mediora.AI surfaces an M-protein result and shows it with immunoglobulins, calcium and kidney function so the plasma-cell pattern is visible; the interpretation belongs with your specialist team.