**Author Listing - Lead/ Submitting Author (we will be communicating with this individual): Name, Institution, City and State where the work was done. Co-authors will be added in a separate section.**
Qian Wang and Benjamin D. Andress

**Main Body of the Abstract**
Background
New immunoglobulin free light chain (FLC) assays have reached the market in the past years. Despite analytical differences, use free light chain ratios (FLCr) generated by different assays and apply similar cut-points for diagnosis of multiple myeloma seems possible. However, using different assays for risk stratification in monoclonal gammopathy of undetermined significance (MGUS) patients remains unknown.
Methods
Patients diagnosed with MGUS (n=923) had FLC testing done using a nephelometric FreeLite (Binding Site) on BNII instruments (Siemens) and Sebia FLC assays (Sebia) on a DS2 ELISA analyzer (Dynex). Patients were followed-up for progression to any plasma cell dyscrasia (PCD) for several decades. The Mayo MGUS risk stratification model for progression was assessed with both assays (M-spike > 1.5g/dL; non-IgG isotype and abnormal FLCr), using package insert reference intervals (RI) and a new metric called principal component 2 (PC2).
Results
There were 94 events of progression to PCD in the cohort during a median of 38 years of follow-up (range 0-47 years). Freelite and Sebia FLC showed similar hazard ratios in the risk models when elevated FLCr were present. When low FLCr was present, Sebia’s RI was not significant. An alternative clinical decision point lower than the RI was evaluated as a risk factor, which improved patients’ stratification. The PC2 metric showed similar performance to the FLCr in models, without superior benefit.
Conclusions
We have demonstrated that a new ELISA based FLC assay can be employed in MGUS risk stratification models with similar performance to the reference assay.



Comparison of two free light chain assays: performance of the free light chain ratio as risk factor for MGUS progression PA103 (#479)

We invite you to attend the XIX International Symposium on Amyloidosis to be held in Rochester, MN.

This symposium is organized as a hybrid meeting (with the focus on in-person) held from Sunday, May 26 through Thursday, May 30, 2024.

Together with the ISA Board and members of Mayo Clinic, a very attractive scientific hybrid program is being planned. The program will cover a variety of types of systemic amyloidosis: ATTR (hereditary and wild-type), AL (light-chain), AA and less frequent forms. There will be key lectures, specific symposia including those company sponsored, oral presentations and poster sessions of accepted abstracts.

COURSE DESCRIPTION
This program will provide a comprehensive review of state-of-the-art education in systemic amyloidosis: basic science, pathophysiology, diagnosis, current and emerging treatments. Scientific presentations will include competitive oral and poster abstracts. The rapid evolution of scientific discovery and expanding treatment options has created tremendous interest in the field and this meeting will fill and important gap in educating scientists and clinicians.