Analysis of serum free light chains by crossed immunoelectrophoresis: comparison with urinary light chains in light chain disease.

We investigated the relationship between serum free light chain levels measured by crossed immunoelectrophoresis in ten patients with light chain disease and traditional 24-hour urinary light chains in the same patients. The crossed immunoelectrophoresis test requires only a venipuncture for specimen acquisition, can be completed within 24 hours, and has a reproducibility (+/- 14%) comparable with that of other immunoprecipitin techniques. Twenty-eight serum-urine pairs, representing 18 discrete intervals, were analyzed. There was a close relationship between changes in serum and urine light chain levels, with a correlation coefficient of .77 or .93, depending on the method of calculation. This suggests that serum light chain levels measured by crossed immunoelectrophoresis would be equivalent to urinary light chain levels as indicators of tumor burden. Monitoring serum levels would have the advantage of greatly simplified specimen acquisition. In patients with renal failure, serum light chain levels should be a superior indicator of light chain synthesis.