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Laboratory Evaluation

As mentioned previously, the cancerous plasma cells of patients with multiple myeloma produce an abundance of a monoclonal protein (M protein) which can be detected in the bloodstream by special techniques called serum protein electrophoresis and immunofixation. In about 80% of patients, the M protein can be detected in the bloodstream (serum) by these techniques. Up to 20% of patients, however, produce a partial M protein monoclonal antibody called a light chain that can only be detected in the urine. When multiple myeloma is suspected, it is, therefore, important to test for the M protein in both serum and urine by protein electrophoresis and immunofixtion.

In about 3% of patients with multiple myeloma, the M protein cannot be detected in either serum or urine with the standard immunofixation technique. In these patients, another test known as serum free light chain assay is useful for both diagnosis as well as for monitoring the patient's response to treatment.

Detection of the M protein is critical for the laboratory diagnosis of multiple myeloma. Other laboratory tests that may be performed on the blood of patients with suspected multiple myeloma include:

• Complete blood counts (CBS) plus differential and platelet counts
• Serum calcium and albumin levels
• Quantitative immunoglobulin testing
• Beta-2 microglobulin levels
• Blood urea nitrogen (BUN) and serum creatinine levels to measure kidney function
• C-reactive protein test
• Lactate dehydrogenase levels

A bone marrow biopsy is usually obtained from patients with suspected multiple myeloma and the specimen is examined for:

• Microscopic evidence of a plasma cell tumor (plasmacytoma)
• Myeloma cell labeling index - a test for measuring how fast the cancerous plasma cells are growing
• Cytogenetic testing - a test performed to detect chromosomal abnormalities

Imaging Studies

Skeletal (bone) abnormalities are detected by conventional X-rays in about 80% of patients with multiple myeloma. Skeletal abnormalities in patients with multiple myeloma are due to increased bone resorption activity by cells called osteoclasts which break down bone at a much faster rate than new bone can be produced by cells called osteoblasts. The net result is bone loss which results in osteoporosis (weak or brittle bones) and an increased risk of fracturs.

Imaging studies to detect skeletal abnormalities may include:

• Skeletal survey - convetional X-rays of the bones
• Magnetic resonance imaging (MRI) to detect spinal cord compression
• Computed Tomography (CT) scan