Serum Protein Electrophoresis (SPEP)
Lab Test Interpretation Pearls for the Nurse Practitioner
Case: You're evaluating a 70-year-old male presenting with fatigue and unintentional weight loss. Given this concerning presentation, it is essential to rule out various underlying causes, including multiple myeloma—a blood cancer originating in plasma cells within the bone marrow.
One key diagnostic test for multiple myeloma is serum protein electrophoresis (SPEP).
The clinical utility and interpretation of SPEP can be tricky – so I hope this article helps!
What is serum protein electrophoresis? (In simple terms)
SPEP analyzes specific blood serum proteins, including albumin and globulins (alpha-1, alpha-2, beta, and gamma), each with distinct physiological roles in the body (1). It detects abnormal protein levels, such as myeloma protein in multiple myeloma (1).
What is Immunofixation vs. Immunofluorescence?
Further separation of different subsets of proteins is done by tests called immunofluorescence and immunofixation (1). Immunofluorescence is ordered for suspected autoimmune disease diagnosis, while Immunofixation confirms monoclonal proteins in plasma cell disorders. These tests are typically ordered after an abnormal SPEP, or in combination with SPEP, depending on your differential diagnosis. (See table below for further information on clinical utility of these tests).
Clinical Applications of SPEP
SPEP helps detect abnormal protein production in plasma cell disorders and systemic diseases, assisting in the diagnosis and monitoring of conditions like multiple myeloma, chronic infections, liver disease, and autoimmune disorders (1,2). Clinical indications for ordering SPEP may include:
Suspected multiple myeloma: patients presenting with weight loss, fatigue, hypercalcemia, new onset anemia with renal insufficiency, bone pain, bence jones proteinuria (2)
Primary amyloidosis: disorder of protein misfolding and metabolism in which insoluble fibrils are deposited in various tissues, causing organ dysfunction (3)
Waldenström’s macroglobulinemia: a type of non-Hodgkin lymphoma where cancer cells make large amounts of macroglobulin
Unexplained peripheral neuropathy: not attributed to diabetes mellitus, chemotherapy, toxin exposure, etc.
Unexplained fragility or pathological fracture, osteolytic lesions
Recurrent infections to screen for immunodeficiency
(*This is not an exhaustive list)
BOTTOM LINE: SPEP is useful for detecting abnormal protein production in plasma cell disorders, however may miss small M-proteins. If SPEP is normal, but your pre-test probability for multiple myeloma is moderate to high, order SPEP with immunofixation.
How does SPEP work?
Blood serum contains two major protein groups: albumin and globulin. Both albumin and globulin carry substances through the bloodstream. Using protein electrophoresis, these two groups can be separated into five smaller groups - albumin, alpha-1, alpha-2, beta, and gamma proteins. The lab separates proteins in the blood based on their size and charge (2). Let’s break down each protein group:
Serum proteins are separated into five main bands:
Albumin: the largest fraction, responsible for maintaining oncotic pressure and transporting substances in the blood (2).
Alpha-1: includes proteins like alpha-1 antitrypsin (inflammation marker), thyroid-binding globulin, and transcortin (2).
Alpha-2: includes ceruloplasmin, alpha2-macroglobulin, and haptoglobin linked to inflammation and liver function) (2).
Beta-1: contains transferrin and complement proteins (immune response, iron transport) (2).
Beta-2: contains beta-lipoprotein, IgA, IgM, and sometimes IgG along with compliment proteins (2).
Gamma: consists of immunoglobulins (antibodies, key for immune function). C-reactive protein is found between beta and gamma components (2).
Normal distribution of proteins with SPEP
SPEP Limitations
It is not sensitive when the M-protein is small, and it cannot classify the type of M protein. In other words, if the SPEP result is normal, but your pre-test probability for multiple myeloma or other plasma cell disorder is moderate to high, further tests such as immunofixation should be ordered (3).
Clinical Applications of Immunofixation vs. Immunofluorescence
(1,2)
How do you Interpret SPEP Results?
The lab evaluates protein pattern, noting if it is normal or abnormal and may recommend further tests like immunofixation. It is critical to watch for and understand the following results:
Monoclonal gammopathy: identified by a distinct spike (M-spike) in the gamma-globulin region on SPEP (2). This spike indicates the overproduction of a single type of immunoglobulin by a single clone of plasma cells, which can be associated with conditions like multiple myeloma or plasma cell leukemia (2).
Polyclonal gammopathy: a broad, diffuse increase in gamma-globulins indicating the overproduction of multiple immunoglobulin types by different plasma cell clones (1, 2). Unlike monoclonal gammopathy, which shows a sharp M-spike, polyclonal gammopathy reflects a general immune activation rather than a single plasma cell clone disorder (2).
Abnormal spike in gamma region of SPEP, indicating monoclonal gammopathy, seen in multiple myeloma.
The following table can help interpret SPEP patterns found in practice.
(2)
BOTTOM LINE:
Monoclonal gammopathy (M spike) → Think multiple myeloma, MGUS (monoclonal gammopathy of undetermined significance), and other plasma cell malignancies (4).
Polyclonal gammopathy → Common in chronic inflammation, infections, or liver disease, rarely malignant (4).
Back to the case: SPEP results reveal a Monoclonal (M) spike in the gamma region.
Next steps
Order Immunofixation Electrophoresis: Confirms the specific type of abnormal immunoglobulin type (IgG, IgA, IgM, etc.) (1,2). It also Distinguishes between different monoclonal gammopathies, such as multiple myeloma, MGUS (monoclonal gammopathy of undetermined significance), or Waldenström's macroglobulinemia (4).
Order Serum Free Light Chains → Checks for abnormal κ (kappa) or λ (lambda) light chain production, which detects plasma cell disorders such as multiple myeloma, MGUS, or amyloidosis (4).
Consider 24-hour Urine Protein Electrophoresis (UPEP) → Looks for Bence-Jones proteins (seen in multiple myeloma) (4).
Assess CBC, calcium, renal function, and skeletal survey → Multiple myeloma can cause anemia, hypercalcemia, kidney dysfunction, and bone lesions (4).
Refer to hematology!
Key Take Home Points:
SPEP is useful for detecting abnormal protein production in plasma cell disorders. If SPEP detects monoclonal gammopathy, further testing is needed.
If SPEP is normal, but your pre-test probability for multiple myeloma is moderate to high, order SPEP with immunofixation to detect small M-proteins that SPEP may miss.
Abnormal SPEP patterns are seen with several diseases, therefore interpretation requires pattern recognition and clinical correlation. If in doubt, seek expert consultation!
ReferencesVavricka SR, Burri E, Beglinger C, Degen L, Manz M. Serum protein electrophoresis: an underused but very useful test. Digestion. 2009;79(4):203-10. doi: 10.1159/000212077. Epub 2009 Apr 9. PMID: 19365122.O'Connell TX, Horita TJ, Kasravi B. Understanding and interpreting serum protein electrophoresis. Am Fam Physician. 2005 Jan 1;71(1):105-12. PMID: 15663032.Baker KR. Light Chain Amyloidosis: Epidemiology, Staging, and Prognostication. Methodist Debakey Cardiovasc J. 2022 Mar 14;18(2):27-35. doi: 10.14797/mdcvj.1070. PMID: 35414848; PMCID: PMC8932379.Murray, L.M. Rajkumar, S. V., Connor, R.F (Ed). Laboratory methods for assessing monoclonal proteins. Up To Date.