The Bence Jones Protein test is a highly specialized, definitive test performed on a urine sample (often a 24-hour collection). It detects a specific, abnormal protein 'fragment' that is not found in healthy individuals. This test is the gold-standard, essential marker for diagnosing and monitoring Multiple Myeloma, a cancer of the plasma cells. This is a critical, non-invasive diagnostic test. It provides your doctor with the precise, "yes/no" answer and quantitative data needed to confirm a diagnosis, assess your condition, and build an effective, personalized treatment plan.