Serum neurofilament-light chain (NfL) and glial fibrillary acidic protein (GFAP) measured by single molecule array (SIMOA) are novel biomarkers of multiple sclerosis patients (MS) activity and progression. Its use is limited due to low availability and high costs. ELLA is a cheaper platform with increasing availability. Recently, we compared SIMOA and ELLA platforms to assess serum NfL levels in 203 MS patients from the OFSEP-HD study. There was a strong correlation (Spearman r = 0.86, p < 0.0001) between both platforms. As for SIMOA, serum NfL levels measured by ELLA were correlated with age and EDSS and were significantly higher in active MS, suggesting that these assays are equivalent and can be used in any center for routine care. However, the accuracy of local measures acquired with ELLA has not been determined. The aim os this study is to assess the concordance of multi-site ELLA instruments, accuracy of GFAP measures as compared to SIMOA, and the predictive value of NfL and GFAP measured by ELLA in MS.

Inclusion Criteria:

• Patients from the OFSEP HD cohort.
• At least one native (no thaw-freeze cycle) serum sample in local or in centralized Biological Resource Center

Exclusion Criteria:

• No bio-collection or insufficient sample volume
• No OFSEP minimal sheet at baseline

Patients with MS from the OFSEP HD (NCT03603457) cohort.