According to the American Cancer Society, the first step to diagnose multiple myeloma is finding a monoclonal antibody in the blood. Serum protein electrophoresis (SPEP), a lab test that measures antibodies, can detect a monoclonal antibody. Urine protein electrophoresis (UPEP) and urine immunofixation can also find monoclonal antibodies in urine collected over a 24-hour period.