Blood and CSF were collected for all patients and analyzed in the Nice University Hospital immunology laboratory. Blood and CSF IgG, albumin, and KFLC were measured by turbidimetry with the analyzer Optilite (The Binding Site, Birmingham, UK) using the serum-free light chain immunoassay Freelite (The Binding Site, Birmingham, UK), according to the manufacturer's instructions. Oligoclonal bands were determined by isoelectric focusing on agarose gel using subsequent immunoblotting using IgG-specific antibody staining (Hydrasys platform; Sebia, Lisses, France). Oligoclonal band patterns were evaluated by an experienced biologist and classified as positive (patterns II and III) or negative (other patterns). A cutoff of ≥ 2 CSF-restricted bands was used to define OCB positivity. The determination of intrathecal synthesis of KFLC was evaluated by the calculation of the K-index using the formula:
K-index = (CSF KFLC/serum KFLC)/(CSF albumin/serum albumin). According to previously published data, a K-index of ≥8.9 was considered as positive.17 (link)
K-index = (CSF KFLC/serum KFLC)/(CSF albumin/serum albumin). According to previously published data, a K-index of ≥8.9 was considered as positive.17 (link)