THE URINARY LIGHT-CHAIN LADDER PATTERN - A PRODUCT OF IMPROVED METHODOLOGY THAT MAY COMPLICATE THE RECOGNITION OF BENCE-JONES PROTEINURIA

Objective.-To describe the recently reported urinary light-chain ''lad der'' pattern and to indicate that this phenomenon, which may give ris e to confusion with Bence Jones protein (BJP), may be observed during routine examination of 50-fold concentrated urine samples tested by hi gh-resolution agarose gel electrophoresis and immunofixation. Methods. -Urine samples that were usually submitted for examination for the pre sence of BJP were concentrated 50-fold. Concentrated urine samples wer e subjected to immunoelectrophoresis and agarose gel electrophoresis. Samples that failed to show a BJP on immunoelectrophoresis but which d id show a faint banding pattern in the stained agarose gel were subjec ted to immunofixation. Results.-Samples of urine from 23 patients fail ed to show a distinct BJP. Nevertheless, these samples did show a kapp a, with or without a lambda, light-chain banding pattern. The urine sa mples came from patients with serum M components associated with neopl asms of either plasma cells (n=2) or lymphocytes (n=2) or with M compo nents of undetermined significance (n=6). The remainder came from pati ents with infectious (n=8), inflammatory (n=4), or neoplastic (n=1) pr ocesses. Some of these patients had no apparent renal disease, while o thers had variably altered renal function. Conclusions.-The urinary li ght-chain ladder pattern was found by routine examination of 50-fold c oncentrated urine samples subjected to agarose gel electrophoresis and immunofixation. The pattern probably reflects the limited heterogenei ty of normal human light chains. Detection in the urine samples of som e patients may reflect increased synthesis, failure of resorption/degr adation in the kidney, or the interference in proximal tubular functio n by substances producing transient tubular proteinuria. The presence of the light-chain ladder pattern in urine may prevent the detection o f small amounts of BJP sharing the electrophoretic mobility of one of the normal light-chain bands.