The urinary light-chain ladder pattern. A product of improved methodology that may complicate the recognition of...

--To describe the recently reported urinary light-chain "ladder" pattern and to indicate that this phenomenon, which may give rise to confusion with Bence Jones protein (BJP), may be observed during routine examination of 50-fold concentrated urine samples tested by high-resolution agarose gel electrophoresis and immunofixation.

--Urine samples that were usually submitted for examination for the presence of BJP were concentrated 50-fold. Concentrated urine samples were subjected to immunoelectrophoresis and agarose gel electrophoresis. Samples that failed to show a BJP on immunoelectrophoresis but which did show a faint banding pattern in the stained agarose gel were subjected to immunofixation. RESULTS--Samples of urine from 23 patients failed to show a distinct BJP. Nevertheless, these samples did show a kappa, with or without a lambda, light-chain banding pattern. The urine samples came from patients with serum M components associated with neoplasms of either plasma cells (n = 2) or lymphocytes (n = 2) or with M components of undetermined significance (n = 6). The remainder came from patients with infectious (n = 8), inflammatory (n = 4), or neoplastic (n = 1) processes. Some of these patients had no apparent renal disease, while others had variably altered renal function. CONCLUSIONS--The urinary light-chain ladder pattern was found by routine examination of 50-fold concentrated urine samples subjected to agarose gel electrophoresis and immunofixation. The pattern probably reflects the limited heterogeneity of normal human light chains. Detection in the urine samples of some patients may reflect increased synthesis, failure of resorption/degradation in the kidney, or the interference in proximal tubular function by substances producing transient tubular proteinuria. The presence of the light-chain ladder pattern in urine may prevent the detection of small amounts of BJP sharing the electrophoretic mobility of one of the normal light-chain bands.