Merck Manuals, an online medical library, reports that multiple myeloma is a form of cancer in which plasma cells become cancerous. Plasma cells are a relatively rare type of blood cell, making up less than 1 percent of total blood cells. However, they are important in fighting off infections because they produce antibodies that attack the invading germs. There are multiple diagnostic criteria to diagnose this type of cancer.
Blood and Urine Tests
One set of diagnostic criteria, described by the Mayo Clinic, is lab testing of the blood and urine. Doctors commonly look for the presence of a protein called "M protein," a type of protein produced in very high amounts by cancerous plasma cells, in blood and/or urine. Additional blood tests are necessary for diagnosis, such as a blood test for beta2-microglobulin, another protein produced by plasma cells. Doctors may also do a lab test that measures the amount of plasma cells in the blood. Because plasma cells are usually relatively rare, a high percentage of plasma cells in the blood would indicate abnormal growth of this cell type, which is a possible indication of cancer. The National Cancer Institute adds that doctors will also test for calcium levels in the blood. Because very high levels of M protein can lodge in the kidney and cause kidney damage, they may also check kidney function by checking for a protein called creatine.
Imaging
Merck Manuals reports that cancerous plasma cells often collect in bones and form tumors. The growth of these tumors can cause bone weakness and even fractures. Because of these complications, the National Cancer Institute reports that another diagnostics test for multiple myeloma is taking images of the body to detect the bone tumors. For example, a whole-body x-ray may be taken, which can help determine the presence of tumors, and show how severely the disease has progressed by the number and sizes of tumors throughout the body. The Mayo Clinic adds that the doctor may order other imaging tests to get a closer look at the bones, such as magnetic resonance imaging (MRI), positron emission tomography (PET) or computerized tomography (CT). These forms of imaging provide a highly detailed image of the bone.
Biopsy
The National Cancer Institute notes that another way to test for multiple myeloma is a biopsy to remove tissue that is suspected of being cancerous. To diagnose multiple myeloma, the biopsy is usually taken from the bone marrow, where the plasma cells often collect. Local anesthesia is administered to numb the area and reduce the pain caused by the procedure. A pathologist looks at the cells under a microscope to provide a firm diagnosis of multiple myeloma based on the presence or absence of cancerous plasma cells.
