ORIGINAL ARTICLEElimination of the Need for Urine Studies in the Screening Algorithm for Monoclonal Gammopathies by Using Serum Immunofixation and Free Light Chain Assays
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PATIENTS AND METHODS
We searched the dysproteinemia database for the first results of all Mayo Clinic patients with a monoclonal gammopathy and a positive urine monoclonal protein on immunofixation who also had serum PE, IFE, and FLC performed within 30 days of diagnosis. We identified 405 patients who were first diagnosed and tested between March 18, 2002, and March 9, 2006. In addition, there were 23 previously diagnosed patients whose initial diagnostic sera were frozen, whose physician had requested serum FLC
RESULTS
In an effort to determine whether urine studies contributed to the diagnostic sensitivity of serum PE, IFE, and FLC, we identified patients with monoclonal gammopathies whose initial urine IFE results indicated a monoclonal protein and who also had serum studies performed. This strategy allowed us to identify patients who had a monoclonal protein in the urine that would have been missed if only serum studies had been performed. The search identified 428 patients with a urinary monoclonal
DISCUSSION
The laboratory contribution to the diagnosis of monoclonal gammopathies has relied on serum and urine PE and IFE. For monoclonal light chain diseases (AL, LCDD) and nonscretory MM, the serum FLC assay is a more sensitive diagnostic test than serum IFE. Because of this increased diagnostic sensitivity, the serum FLC assay is a reasonable addition to diagnostic algorithms. It has been reported that, if a monoclonal light chain is detected by IFE in the serum or urine, then the serum FLC assay is
CONCLUSION
A diagnostic algorithm with use of only serum studies (PE, IFE, and FLC quantitation) missed 2 (0.5%) of the 428 monoclonal gammopathies with urinary monoclonal proteins. These 2 cases required no medical intervention. The discontinuation of urine studies from the screening algorithm resulted in a minimal loss of diagnostic sensitivity.
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This work was supported in part by research grants CA107476 and CA62242 from the National Cancer Institute.