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BACKGROUND: Neurofilament light chain (Nf-L) is a key early biomarker for axonal damage and neurodegeneration, increasingly used in clinical practice for diagnosis, prognosis, and treatment monitoring. To ensure reliable clinical implementation, standardized measurement procedures and calibrators traceable to the International System of Units (SI) are needed. Although a few mass-spectrometry methods for Nf-L quantification in cerebrospinal fluid CSF) and plasma have been described, none currently use properly defined SI-traceable calibrators and existing harmonization efforts rely solely on immunoassays. This study presents a validated immunoprecipitation (IP)-LC-MS/MS assay using an SI-traceable calibrator and compares it with Lumipulse and Simoa platforms to assess agreement and bias. METHODS: A new IP-LC-MS/MS method was developed based on SI-traceable calibrator quantification and analytically validated using International Council for Harmonisation (ICH) guidelines. Analysis of 69 CSF samples by MS assay and Lumipulse (Fujirebio®) was performed as well as head-to-head comparisons between MS, Simoa (Quanterix®) and Lumipulse assays on 12 CSF pools. RESULTS: The method relying on 3 peptides was validated analytically. Significant results (P 0.98) but systematic bias was identified between all techniques. CONCLUSION: A new IP-LC-MS/MS method using a SI-traceable calibrator was developed, and analytically and clinically validated. Comparison between available immunoassays resulted in great correlation but biases were identified reinforcing the need of standardization for Nf-L measurement.
Coppens et al. (Tue,) studied this question.