Multiple Myeloma Blood Test Results Explained: What They Mean
Also known as: multiple myeloma test, myeloma blood work, M protein test
Multiple myeloma blood tests look for abnormal antibody proteins (M proteins) made by cancerous plasma cells, plus effects on calcium, kidneys, and blood counts. Key tests include serum protein electrophoresis (SPEP) and free light chains. Abnormal results strongly suggest myeloma, but a bone marrow biopsy is needed to confirm it.
How blood tests are used
Myeloma often shows a distinctive pattern: a spike of one abnormal protein, sometimes with high calcium, anemia, and reduced kidney function (the 'CRAB' features). Blood and urine protein tests are central to detection, but diagnosis is confirmed with bone marrow testing and imaging.
Key multiple myeloma blood tests
| Test | What it checks |
|---|---|
| SPEP (serum protein electrophoresis) | Detects an abnormal 'M spike' of monoclonal protein. |
| Serum free light chains | Measures kappa/lambda light chains; an abnormal ratio suggests a plasma cell disorder. |
| Immunofixation | Identifies the exact type of abnormal antibody protein. |
| Calcium | May be high (hypercalcemia) in myeloma. |
| Creatinine / eGFR | Assesses kidney function, which myeloma can impair. |
| CBC | May show anemia. |
What the results mean
- An M spike on SPEP or an abnormal free light chain ratio strongly suggests a plasma cell disorder.
- High calcium, anemia, and reduced kidney function together raise concern for active myeloma.
- Abnormal blood tests are followed by a bone marrow biopsy and imaging to confirm and stage the disease.
- Small amounts of abnormal protein without other features may indicate a benign precursor (MGUS) that is monitored.
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Frequently asked questions
What blood tests detect multiple myeloma?
The main tests are serum protein electrophoresis (SPEP), which looks for an abnormal 'M protein' spike, and serum free light chains. These are often paired with calcium, kidney function (creatinine/eGFR), and a CBC. Abnormal results are confirmed with a bone marrow biopsy.
What is an M spike?
An M spike (monoclonal spike) is an abnormal surge of a single antibody protein produced by cancerous plasma cells, seen on serum protein electrophoresis. It's a hallmark of myeloma and related disorders, though small spikes can also occur in the benign condition MGUS, which is monitored over time.
Can myeloma be found on a routine blood test?
Sometimes. Routine tests may reveal clues like high total protein, high calcium, anemia, or impaired kidney function, prompting specific myeloma testing. But dedicated protein studies (SPEP, free light chains) and a bone marrow biopsy are needed to diagnose it.
Related biomarkers
Medically reviewed by Antonieta Rueda, MD and Ayham Shneker, MD · Last reviewed July 6, 2026
This article is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Blood tests are interpreted by a clinician alongside your symptoms and history. Always consult your healthcare provider about your results.