**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.**
Paolo Milani, Department of Molecular Medicine, University of Pavia, Amyloidosis Research and Treatment Center, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy

**Main Body of the Abstract**
New reference ranges for serum free light chain ratio (FLCR) that consider age and estimated glomerular filtration rate (eGFR) have been recently proposed in the iSTOPMM study. We compared the performance of the new and old reference ranges in patients with light chain (AL) and transthyretin wild-type (ATTRwt) amyloidosis. The Freelite assay was used.
A total of 1705 patients with established AL amyloidosis diagnosed between 2004 and 2021, and 675 patients with established ATTRwt diagnosed between 2006 and 2021 were included. The results in the AL cohort are reported in the Table. Amongst patients with AL amyloidosis who obtained negative serum and urine immunofixation after therapy, the definition of complete response was concordant in 97.3% (95% CI 96.1-98.2%) of patients with no difference in overall survival between the newFLCR-CR and oldFLCR-CR groups.
In the ATTRwt cohort, a total of 84 had positive serum and/or urine immunofixation (IFE). In these subjects the new and old FLCR were abnormal in 15 (18%) and 35 (41%) of cases, respectively. In patients with negative serum and urine IFE, the new and old FLCR were abnormal in 14 (2%) and 156 (23%) of cases, respectively.
The new reference range for FLCR reduces the sensitivity for kappa and increases the sensitivity for lambda clones in AL amyloidosis. Overall, this does not affect assessment of CR and does not decrease the diagnostic sensitivity in AL amyloidosis. In patients with ATTRwt amyloidosis, the new FLC ratio substantially reduces the proportion of patients who need a biopsy-based diagnosis.



New reference ranges of free light chain ratio: impact on clinical practice in AL and ATTRwt amyloidosis PB83 (#443)

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.