This study aims to guide the integration of serum free light chain (sFLC) tests into clinical practice, including a new rapid test (Seralite(®) ). Blood and urine analysis from 5573 newly diagnosed myeloma patients identified 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(®) sFLC ≥100 mg/l for measuring response was confirmed and the equivalent Seralite(®) FLC difference (dFLC) >20 mg/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 at least a very good partial response according to either sFLC method was associated with better patient survival. Relapse was identified using a Freelite(®) sFLC increase >200 mg/l and found 100% concordance with a corresponding Seralite(®) dFLC increase >30 mg/l. Both Freelite(®) and Seralite(®) sensitively diagnose and monitor LCO/oligosecretory myeloma. Rapid testing by Seralite(®) could fast-track FLC screening and monitoring. Response by sFLC assessment was prognostic for survival and demonstrates the clinical value of routine sFLC testing.
- Journal Article