The clinical significance of Bence Jones proteinuria

The detection of monoclonal light chains in the urine by the Bence Jones heat test is a useful adjuvant to the diagnosis of myeloma and other related diseases. The test is particularly helpful when no serum spike is noted. Overall, it is positive in approximately half of all patients with myeloma. In order to assess the accuracy of the test, we reviewed the records of all patients with a positive heat test for Bence Jones proteinuria during a single calendar year. Myeloma accounted for 68%, but patients with amyloidosis, the adult Fanconi syndrome, and others also had positive results. One-fifth of the results were false positive in that urine protein electrophoresis showed no spike and immunoelectrophoresis, no monoclonal protein. This group consisted largely of patients with connective tissue diseases, chronic renal failure, or nonplasmacytic malignancies. We also have seen patients who had monoclonal light chains in their urine but failed to show positive results to the heat test and were thus considered false negative. Although the heat test for Bence Jones proteins is a useful clinical test, one must be aware of both false-positive and false-negative results. Electrophoresis and immunoelectrophoresis of concentrated urine are the methods of choice for detection of a monoclonal light chain in the urine.