PRTN3 and rheumatoid arthritis: Although we considered an anti-CCP titer ≥ 100 to be 100, the relationship between the anti-CCP antibody titer and the risk of developing RA is supported by patients with a high ACPA level having a high score in the 2010 ACR/EULAR classification criteria of RA [26] as well as a high anti-CCP antibody titer being more strongly associated with RA in the general population [32].