Assessing Serum Neurofilament Light Chain in Hereditary Transthyretin Amyloidosis: Direct Comparison of Three Immunoassays

<b>Background/Objectives</b>: Serum neurofilament light chain (sNfL) is an early and sensitive biomarker of polyneuropathy. This study compared the UmanDiagnostics enzyme-linked immunosorbent assay (ELISA), and Meso Scale Discovery (MSD) R-PLEX assay with the current gold-standard single-molecule array (Simoa) assay for sNfL measurement. <b>Methods</b>: sNfL levels were measured with Simoa, ELISA, and MSD R-PLEX in 330 serum samples from 73 individuals with a pathogenic transthyretin gene variant (<i>TTR</i>v) and in 165 healthy controls (HC) with ELISA and MSD R-PLEX. <b>Results</b>: Median sNfL levels, assessed in serum samples from <i>TTRv</i> individuals, differed across all assays (all <i>p</i> < 0.001). Passing-Bablok regression slopes were 1.01 (Simoa-ELISA), 1.00 (Simoa-MSD R-PLEX), and 1.02 (MSD R-PLEX-ELISA), with very strong correlations (all r > 0.8). Bland-Altman analysis showed mean differences of 0.1 ± 0.2 pg/mL (Simoa-ELISA), 0.7 ± 0.1 pg/mL (Simoa-MSD R-PLEX), and -0.6 ± 0.2 pg/mL (MSD R-PLEX-ELISA). In HC, sNfL levels positively correlated with age. Z-score normalization allowed for inter-assay comparison. <b>Conclusions</b>: The ELISA and MSD R-PLEX assays provide suitable alternatives for the Simoa assay to measure sNfL levels in carriers of a pathogenic <i>TTR</i>-gene variant. The differences in concentrations defined by the assays directly relate to the internal standard provided with the assays.