This study aims to guide integration of serum FLC (sFLC) tests into clinical practice, including a new rapid test (Seralite®). Blood and urine analysis from 5573 newly diagnosed myeloma patients provided 576 light chain only (LCO) and 60 non-secretory (NS) cases. Serum was tested by Freelite® and Seralite® at diagnosis, maximum response and relapse. 20% of LCO patients had urine FLC levels below that recommended for measuring response but >97% of these had adequate sFLC levels (oligosecretory). The recommended Freelite® FLC >100mg/L for measuring response was confirmed and equivalent Seralite® FLC difference (dFLC) >20mg/L identified. By both methods, ≥ 38% of NS patients had measurable disease (oligosecretory). Higher sFLC levels were observed on Freelite® at all time points. However, good clinical concordance was observed at diagnosis and in response to therapy. Achieving ≥ VGPR, according to either sFLC method, was associated with better patient survival. Relapse was identified using a Freelite® sFLC increase >200mg/L and found 100% concordance with a corresponding Seralite® dFLC increase >30mg/L. Both Freelite® and Seralite® sensitively diagnose and monitor LCO/oligosecretory myeloma. Rapid testing by Seralite® could fast-track FLC screening/monitoring. Response by sFLC assessment was prognostic for survival and demonstrates the clinical value of routine sFLC testing.
- free light chains
- multiple myeloma