Serum free light chain measurements to reduce 24‐h urine monitoring in patients with multiple myeloma with measurable urine monoclonal protein

Marcella Tschautscher, Vincent Rajkumar, Angela Dispenzieri, Martha Lacy, Morie Gertz, Francis Buadi, David Dingli, Lisa Hwa, Amie Fonder, Miriam Hobbs, Suzanne Hayman, Stephen Zeldenrust, John Lust, Stephen Russell, Nelson Leung, Pranshant Kapoor, Ronald Go, Yi Lin, Wilson Gonsalves, Taxiarchis Kourelis, Rahma Warsame, Robert Kyle, Shaji Kumar

Detection of myeloma progression (PD) relies on serial 24-hr urinary M protein measurements in patients without measurable serum M spike. We examined whether serial dFLC levels could be used as a surrogate for serial 24-hr urine M protein measurements in monitoring for PD in patients with baseline measurable urine M protein. We studied 122 patients who had serial measurement of urine M protein and serum FLC and had demonstrated PD. The median increase in dFLC with progression as defined by urine M spike was 110% (IQR: 55-312) and median absolute increase was 74mg/dL; while 89% of patients had dFLC increase>25%, 94% had absolute increase in dFLC>10mg/dL, and 98% met at least one of these two criteria at PD. In patients with baseline measurable sFLC (n=118), 89% had increase in dFLC>25%, 97% had dFLC increase of >10 mg/dL, and 98% had one of the two. We conclude that serial dFLC assessments can be used in place of serial 24-hour urine protein assessments during myeloma surveillance to monitor for PD. Once patients have an absolute increase in dFLC of >10 mg/dL from the nadir, a 24-hour urine collection can then be assessed to document PD as per the IMWG criteria. This article is protected by copyright. All rights reserved.