Bence-jones proteins These are free monoclonal light chains (Remember that immunoglobulins are composed of two different types of polypeptide chains, heavy and light. Heavy chains determine immunoglobulin class whereas light chains are common amongst the classes and consist of lambda and kappa chains). Free polyclonal light chains (i.e. consisting of both lambda and kappa chains) are produced by all plasma cells. A small amount of these polyclonal light chains may be observed in urine from healthy patients and are increased if there is tubular dysfunction (free light chains have molecular weights < 44,000 daltons and are filtered by the glomeruli and catabolized by proximal renal tubule cells). In plasma cell disorders, such as multiple myeloma, free light chains are produced in excess and are monoclonal in nature (either kappa or lambda, not both). These free monoclonal light chains are called B-J and appear in the urine. They can be detected in urine in two ways: Heat precipitation: B-J display unique solubility characteristics. As urine is heated, they precipitate at approximately 56 C. They dissolve at 100 C. When urine is cooled, they re-precipitate at 56 C. In theory, this should work quite well. However, in practice, many patients with myeloma have renal dysfunction (myeloma kidney) and have albuminuria. Albumin precipitates at 100 C and does not re-dissolve, complicating interpretation of the test. Furthermore, not all canine or feline patients have urinary B-J (approximately 10-40% of canine myeloma patients have urinary B-J). Urine electrophoresis: B-J proteins can be detected on urinary electrophoretograms. These should always be interpreted in conjuction with a serum electrophoretogram. Once again, interpretation is confounded by albuminuria as a monoclonal peak in urine could represent heavy chain as well as light chain. In human patients, B-J proteinuria is confirmed by immunofixation using specific light chain antisera to confirm monoclonality. Unfortunately, suitable reagents are not available for veterinary patients to be able to perform this test. Remember that urinary dipsticks do not detect B-J, but sulfosalicylic acid will precipitate B-J as well as other urinary proteins.