AREG and rheumatoid arthritis: Although there was no significant difference between the levels of HB-EGF in the RA and OA samples, its high correlations with AREG and EREG (ρ = 0.788, P = 0.0008 and ρ = 0.823, P = 0.0005, respectively) imply that HB-EGF may be upregulated in RA.