How To Diagnose Multiple Myeloma? Guide

Multiple myeloma is a cancer of plasma cells, a type of white blood cell that normally makes antibodies. It is diagnosed through a combination of blood and urine tests, imaging, and a bone marrow biopsy. No single test confirms it. Doctors look for specific patterns across several results, and the diagnosis usually comes from a hematologist or oncologist rather than a primary care visit alone.

That process matters because myeloma can be slow to reveal itself. Early symptoms like fatigue or back pain are common and usually have other causes. The tests below are how doctors sort a vague complaint from a disease that needs treatment.

How To Diagnose Multiple Myeloma: What Tests Do Doctors Use?

Diagnosis rests on four pillars: blood tests, urine tests, imaging, and bone marrow examination. Each answers a different question, and together they show whether abnormal plasma cells are present and whether they are causing harm.

Blood tests are usually the starting point. A complete blood count can show low red blood cells, low white blood cells, or low platelets. A chemistry panel checks calcium and kidney function, both of which can be affected by myeloma. The most specific blood test measures M protein — an abnormal antibody fragment produced by cancerous plasma cells. It is often detected with a test called serum protein electrophoresis, sometimes paired with immunofixation to identify the exact type.

A related test measures free light chains, the smaller antibody pieces that plasma cells make. Some myelomas produce light chains but little or no intact M protein, so this test catches cases that electrophoresis alone might miss.

Urine tests look for Bence Jones protein, which is free light chains filtered into the urine. A 24-hour urine collection is often used.

Imaging looks for bone damage. Myeloma causes lytic lesions — areas where bone has been eaten away without new bone forming. A whole-body low-dose CT scan or MRI is commonly used. PET-CT may be used in some situations. Standard X-rays are less sensitive than these newer methods and are used less often now for this purpose.

Bone marrow biopsy is the definitive step. A doctor removes a small sample of marrow, usually from the hip bone, and a pathologist examines it to measure the percentage of plasma cells and look for abnormal features. This test also helps rule out other conditions that can mimic myeloma.

What Are the CRAB Criteria and Why Do They Matter?

Finding abnormal plasma cells is not enough to diagnose symptomatic myeloma. Doctors need evidence that the disease is causing organ damage. That evidence is organized around four features known by the acronym CRAB.

• C — Calcium: Elevated blood calcium, typically above 11 mg/dL, caused by bone breakdown.
• R — Renal: Kidney damage, often reflected in a creatinine level of 2 mg/dL or higher or a reduced eGFR.
• A — Anemia: Low red blood cells, generally a hemoglobin below 10 g/dL or more than 2 g/dL below normal.
• B — Bone: One or more lytic bone lesions seen on imaging.

These thresholds come from established diagnostic criteria used worldwide. They are not arbitrary. Each represents a point at which the disease is measurably harming the body and treatment is generally indicated.

There are also three “biomarker” events that count as myeloma-defining even without CRAB features: a very high percentage of clonal plasma cells in the marrow (60% or more), a skewed free light chain ratio (100 or greater), or more than one MRI-detected lesion of a certain size. These were added because studies showed people meeting them develop symptoms quickly.

What Is the Difference Between MGUS, Smoldering Myeloma, and Active Myeloma?

Not everyone with abnormal plasma cells has cancer that needs treatment. This is one of the most important distinctions in the diagnostic process, and it is the reason a bone marrow biopsy and careful follow-up matter.

MGUS — monoclonal gammopathy of undetermined significance — is common and not cancer. A small M protein is present, plasma cells are below 10%, and there is no organ damage. A small fraction of people with MGUS progress to myeloma each year, so regular monitoring is typical.

Smoldering myeloma sits in between. The numbers are higher, but there is still no organ damage. Most people are watched closely rather than treated immediately, though this is an area where practice has been shifting as research evolves. Some high-risk patients may be offered treatment earlier in certain settings. That decision belongs with a specialist.

Active myeloma means the disease is causing harm or meets biomarker criteria. This is when treatment begins.

What Symptoms Should Prompt Testing?

Myeloma symptoms are often vague, and many people have no symptoms at diagnosis — the disease is sometimes found on routine blood work showing high protein or anemia. When symptoms do appear, they tend to reflect the CRAB features.

Bone pain is common, especially in the back or ribs. It is often described as persistent rather than sharp. Fatigue from anemia is frequent. Repeated infections can occur because normal antibodies are crowded out by the abnormal ones. Kidney problems may show up as swelling, foamy urine, or changes in urination. Unexplained weight loss and confusion from high calcium are also possible.

None of these symptoms points to myeloma on its own. Back pain is far more often mechanical. Fatigue has dozens of causes. The reason doctors test for myeloma is the pattern — several of these together, or a lab result that does not fit.

One clarification worth knowing: myeloma does not usually cause a lump you can feel. It lives in the bone marrow, not in soft tissue. When it does form a mass outside bone, that is called a plasmacytoma, and it is diagnosed differently.

Who Should Be Tested and Who Should Not?

There is no routine screening test for myeloma in the general population. Guidelines do not recommend checking everyone for M protein. The tests are used when there is a reason.

Testing is reasonable when someone has unexplained anemia, elevated calcium, kidney problems without a clear cause, bone pain that persists, frequent infections, or a high total protein level on a routine panel. A family history of myeloma or MGUS also raises the index of suspicion, though myeloma is not strongly inherited.

Myeloma is more common in people over 60 and somewhat more common in men and in Black Americans. These are population patterns, not individual predictions. They inform how quickly a doctor might order tests, not whether any one person will develop the disease.

What Happens After a Diagnosis Is Confirmed?

Once myeloma is confirmed, the next step is staging. Staging helps guide treatment and estimate outlook, though it does not determine exactly how any one person will do.

The most widely used system is the Revised International Staging System, which combines blood levels of beta-2 microglobulin and albumin with specific genetic markers found in the bone marrow. Genetic testing of the plasma cells — looking at chromosomes and specific gene rearrangements — is part of the workup because certain abnormalities predict a more aggressive course.

Treatment planning also depends on age, overall health, kidney function, and whether the disease is newly diagnosed or has come back. Modern treatment often combines several drug classes and may include stem cell transplant in eligible patients. That is a separate conversation from diagnosis, and the details change as new drugs are studied.

What matters at the diagnostic stage is getting a complete picture. A partial workup can lead to the wrong label — treating smoldering myeloma as active disease, or missing a case that needs attention. A hematologist should review the full set of results together.