Table 1.

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.