How is Multiple Myeloma Diagnosed? Tests, Criteria & Staging Explained
If you’ve read through the common symptoms of multiple myeloma and recognized a few in yourself or someone close to you, the next question is usually the same one every patient asks: “So how do they actually confirm this?”
It’s a fair question, and the honest answer is — it’s not one single test. Multiple myeloma diagnosis is a step-by-step process that combines blood work, urine tests, imaging, and sometimes a bone marrow biopsy. Each piece adds information the others can’t provide on their own.
This guide walks through exactly what that process looks like, what each test is checking for, and how doctors use the results to confirm a diagnosis and determine its stage. If you haven’t yet, it’s worth understanding when symptoms warrant this kind of evaluation this diagnostic path is what usually follows.
Multiple Myeloma Diagnostic Criteria — How Doctors Confirm It
Multiple myeloma diagnosis relies on a set of internationally recognized diagnostic criteria, not a single lab value. Doctors typically follow the International Myeloma Working Group (IMWG) criteria, which combines blood test findings, bone marrow plasma cell percentage, and evidence of organ damage caused by the disease.
In simple terms, a diagnosis is confirmed when there’s clear evidence of abnormal plasma cells in the bone marrow along with specific markers in the blood or urine, plus signs that the disease is actually causing harm — not just present in small, harmless amounts.
That last part matters more than people realize. It’s the exact reason conditions like MGUS exist as a separate category — abnormal cells can be present without meeting the threshold for active disease.
CRAB Criteria Explained
The CRAB criteria is a set of four clinical findings doctors use to determine whether multiple myeloma is causing active organ damage:
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- C – Calcium elevated (Hypercalcemia): High calcium levels in the blood, often due to bone breakdown
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- R – Renal impairment: Reduced kidney function, frequently caused by abnormal protein buildup
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- A – Anemia: Low red blood cell counts, usually from bone marrow crowding
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- B – Bone lesions: Areas of bone damage visible on imaging, caused by abnormal plasma cell activity
Meeting even one of these criteria, combined with confirmed abnormal plasma cells, is generally enough to establish a diagnosis of active multiple myeloma rather than an earlier, watch-and-wait stage.
Blood and Urine Tests for Multiple Myeloma
Blood and urine tests are usually the starting point, and for good reason — they’re non-invasive and can reveal a lot before anything more involved is needed.
Serum Protein Electrophoresis (SPEP) and M-Spike
This test separates the different proteins in your blood based on their electrical charge, producing a pattern that a lab can read. In multiple myeloma, this pattern typically shows an unusual spike — referred to as an M-spike — caused by the large quantity of identical, abnormal antibody protein the myeloma cells are producing.
Practically speaking, this single test often gives the first strong hint that something needs closer investigation, well before any imaging is done.
Bence Jones Protein Test
This is a urine test that looks for light chain proteins — fragments of the abnormal antibody that myeloma cells produce. Their presence, particularly in significant amounts, supports a multiple myeloma diagnosis and can also indicate how much strain is being placed on the kidneys.
Bone Marrow Biopsy — What to Expect
A bone marrow biopsy is usually the test patients are most anxious about, and that’s understandable. But it’s worth knowing what it actually involves before assuming the worst.
The procedure involves taking a small sample of bone marrow, typically from the back of the hip bone, using a thin needle under local anesthesia. It’s done as an outpatient procedure, usually takes under 30 minutes, and most patients describe brief discomfort rather than significant pain — not the ordeal it’s sometimes imagined to be.
This test is essential because it directly measures what percentage of plasma cells in the marrow are abnormal, which is a core part of the diagnostic criteria. Blood tests can suggest myeloma, but the bone marrow biopsy is often what confirms it.
Imaging Tests — X-Ray, MRI and Radiology Findings
Imaging plays a specific role here: identifying bone damage caused by myeloma activity, which the CRAB criteria requires as part of confirming active disease.
X-rays are often the first imaging step, looking for what’s known as lytic lesions — small areas where bone has been weakened or eroded, sometimes described as “punched-out” spots on imaging. These are commonly checked in the skull, spine, and pelvis.
MRI and CT scans offer more detail, particularly for the spine, and can pick up on soft tissue involvement or early bone changes that a standard X-ray might miss. In cases where spinal involvement is suspected, an MRI is often preferred for its clarity.
Which imaging is used, and how much of it, usually depends on what the blood tests and clinical picture already suggest — it’s rarely a one-size-fits-all approach.
Staging Multiple Myeloma — Understanding ISS Stages
Once multiple myeloma is confirmed, the next step is staging — which helps determine how advanced the disease is and guides treatment planning. The most widely used system is the International Staging System (ISS), based primarily on two blood markers: Beta-2 microglobulin and albumin.
| Stage | Beta-2 Microglobulin | Albumin |
| Stage I | Less than 3.5 mg/L | 3.5 g/dL or higher |
| Stage II | Between Stage I and III values | — |
| Stage III | 5.5 mg/L or higher | — |
Higher Beta-2 microglobulin levels generally indicate a greater disease burden, while lower albumin levels can reflect the body’s reduced ability to compensate. Stage III doesn’t mean treatment isn’t effective — it simply informs doctors about disease extent, which shapes the treatment approach that follows.
What Happens After Diagnosis?
Once diagnosis and staging are complete, the conversation naturally shifts toward treatment. This is often the point where patients feel the most uncertain, but having a confirmed diagnosis and stage actually gives doctors a much clearer path forward rather than a guessing game.
The specific treatment approach depends on several factors — stage, overall health, and how the disease is behaving — which is covered in our guide on multiple myeloma treatment options .
A note worth reading: This article explains the general diagnostic process for multiple myeloma, but individual cases can vary in which tests are prioritized and in what order. It’s not meant to replace a proper clinical evaluation. If you’re going through this process yourself, don’t hesitate to ask your doctor to explain any result you don’t fully understand — a good diagnostic conversation should never feel rushed.
If you or a loved one are navigating test results or waiting on a diagnosis, consulting Dr. Kunal Chhattani can help bring clarity to what the numbers actually mean and what comes next — explore our complete blood cancer treatment approach for the bigger picture.
FAQ Section (Schema-Ready)
What tests confirm multiple myeloma diagnosis?
Diagnosis typically combines blood tests (like SPEP and M-spike), urine tests for Bence Jones protein, a bone marrow biopsy, and imaging to check for bone lesions — no single test confirms it alone.
What is the CRAB criteria in multiple myeloma?
CRAB stands for Calcium elevated, Renal impairment, Anemia, and Bone lesions — four clinical findings doctors use to confirm active, symptomatic multiple myeloma.
Is bone marrow biopsy painful?
Most patients experience brief discomfort rather than significant pain, since the procedure is done under local anesthesia and typically takes under 30 minutes.
What is an M-spike in blood tests?
An M-spike refers to an abnormal spike seen on serum protein electrophoresis, caused by the large amount of identical antibody protein that myeloma cells produce.
What are the stages of multiple myeloma?
Multiple myeloma is staged using the International Staging System (ISS), which classifies the disease into Stage I, II, or III based on blood levels of Beta-2 microglobulin and albumin.
How long does diagnosis take?
Timeline varies, but blood and urine test results are often available within days, while a full diagnosis including bone marrow biopsy and imaging may take one to two weeks depending on scheduling.
