Patient characteristics
| Total n | Female | Male | Median age (range) | Median ∆t months (range) | |
| IFNβ subgroup t1–t2 | 170 | 106 (62%) | 64 (38%) | 37 (16–58) | 13 (1–59) |
| NAT group t3–t4 | 714 | 500 (70%) | 214 (30%) | 37 (12–63) | 12 (1–38) |
| Blood donors | 144 | 100 (69%) | 44 (31%) | 35 (18–63) |
The analysed serum samples were obtained from patients with multiple sclerosis enrolled in the Swedish pharmacovigilance study for natalizumab (NAT). The interferon beta (IFNβ) subgroup is a subgroup of the NAT group defined by samples available prior to NAT therapy at time point 1 (t1) and t2. The NAT group consists of samples taken before NAT treatment, at t3 and during NAT treatment, at t4. Sex-matched and age-matched blood donors were included as a control group. Δt is duration of time in months between samples taken at t1–t2 and t3–t4.