Real-world Roche Elecsys® and Fujirebio Lumipulse® inter-platform comparability and clinical validation of plasma neurofilament light chain in multiple sclerosis.

BACKGROUND: Neurofilament light chain (NfL) reflects neuro-axonal injury in multiple sclerosis (MS), but method-dependent bias limits interchangeability across automated platforms. We assessed agreement between Roche Elecsys® and Fujirebio Lumipulse®, evaluated Simoa-referenced harmonization, validated Elecsys® clinical associations, and derived directional IVD-to-IVD conversion models between Elecsys® and Lumipulse®. METHODS: In this retrospective real-world cohort (N=253), fasting EDTA plasma was analyzed in singlicate on Elecsys® and Lumipulse®. Clinical associations of Elecsys® pNfL were tested using multivariable linear models, including age, sex, disease duration, EDSS, cardiovascular comorbidities, smoking, and disease course, with sensitivity analyses including BMI. RESULTS: On the raw scale, platforms were strongly correlated but showed poor agreement (Coeff 6.91, 95% CI 6.44-7.38; r=0.879; CCC=0.107, 95% CI 0.090-0.123). After conversion of both assay outputs to published Simoa-equivalent values, alignment improved (Coeff 1.03, 95% CI 0.96-1.10). We derived a directional Elecsys®-to-Lumipulse® Passing-Bablok conversion (Lumipulse = 1.97 + 11.171 × Elecsys). Higher Elecsys® pNfL was associated with disability (EDSS: Coeff 0.302, 95% CI 0.122-0.481; with BMI: Coeff 0.335, 95% CI 0.119-0.551) and was lower in treated versus untreated patients. CONCLUSIONS: Elecsys® and Lumipulse® are not interchangeable on the raw pg/mL scale though conversion-based approaches can improve cross-platform alignment within the observed analytical range. Elecsys® pNfL retained expected clinical associations, supporting routine MS use. Findings support cautious conversion during platform transitions in clinics.