Objectives Compare Elecsys (Roche) and Simoa (Quanterix) immunoassays for serum glial fibrillary acidic protein (GFAP) using our reference database and Z scores, and evaluate their prognostic value for progression independent of relapse activity (PIRA) in multiple sclerosis (MS). Methods Platform correlation was assessed in 612 samples from healthy controls (n=188; median interquartile range, IQR age 45. 1 36. 4–61. 7 years) and people with MS (n=424; 45. 3 35. 2–53. 9 years). Elecsys values were converted to Z scores via Passing-Bablok-derived regression and validated in fingolimod (n=414), and B-cell depleting therapy (BCDT; n=353) cohorts. Z scores and hazard ratios (HRs) for time-to-PIRA were compared using Cox regression. Results GFAP ₒ₈₌₎₀ and GFAP ₄₋₄₂ₒₘₒ measurements were correlated (r=0. 94), with Elecsys values ∼54 % lower (GFAP ₄₋₄₂ₒₘₒ, ng/L=2. 847 95 % confidence interval, CI: 1. 335 – 4. 98 + 0. 457 0. 434 – 0. 478 * GFAP ₒ₈₌₎₀, ng/L). In univariable Cox models, GFAP ₒ₈₌₎₀ and GFAP ₄₋₄₂ₒₘₒ Z scores were associated with time-to-PIRA in both validation cohorts. In multivariable Cox models, higher GFAP ₒ₈₌₎₀ Z scores were associated with shorter time-to-PIRA in fingolimod cohort (HR: 1. 27 95 % CI 1. 08 – 1. 50, p=0. 0031) and trended toward significance in BCDT (1. 18 0. 99 – 1. 41, p=0. 0693). In contrast, GFAP ₄₋₄₂ₒₘₒ Z scores were associated with time-to-PIRA in both cohorts (fingolimod: 1. 27 [1. 09 – 1. 48, p=0. 0023; BCDT: (1. 19 1. 00 – 1. 40, p=0. 0487). Conclusions Serum GFAP measured by Elecsys shows a comparable association with time-to-PIRA as Simoa, and GFAP ₒ₈₌₎₀ Z scores can be successfully bridged to GFAP ₄₋₄₂ₒₘₒ Z scores, supporting Elecsys`s potential for clinical implementation.
Willemse et al. (Mon,) studied this question.