POS0025 INCIDENCE RATES AND POINT PREVALENCE OF SEROPOSITIVE AND SERONEGATIVE RHEUMATOID ARTHRITIS IN DENMARK: A NATIONWIDE REGISTER-BASED STUDY FROM 1998 TO 2018 USING FOUR DIFFERENT CASE CRITERIA

Abstract

Background:Few previous studies have investigated the incidence rate (IR) and point prevalence (PP) of seropositive and seronegative rheumatoid arthritis (RA), and further, the estimates remain unknown in the Danish population.Objectives:To investigate the IR and PP of seropositive and seronegative RA in the adult Danish population from 1998 to 2018 using four register-based case definitions of RA.Methods:Nationwide register-based cohort study. Using the Danish administrative registers, patients with RA between 1998 and end of 2018 were identified. ICD-10 codes for RA were identified in the Danish National Patient Registry and information on DMARD prescriptions were obtained through the Danish National Prescription Registry using ATC codes. The used case definitions were1: Criteria A, first time M05/M06 RA diagnosis and redemption of a DMARD in the following year; Criteria B, two RA diagnoses within 90 days of each other, originating from department of rheumatology or general internal medicine, where the latest registered M05/M06 diagnosis defined the serologic status; Criteria C, a M05/M06 diagnosis recorded at any time preceded or followed by redemption of a DMARD prescription within one year, where the M05/M06 diagnosis recorded determined the serologic status; Criteria D, as Criteria A, but with the additional requirements that cases had no registration for other selected inflammatory diseases.In calculation of IRs the total Danish population from 1998 to 2018 was used as reference population for standardisation. The PP was calculated for years 2000, 2009, 2011 and 2018.Results:From 1998 to 2018 the overall IR was 18.0 (95%CI 17.7 to 18.3) per 100,000 person years (PY) for seropositive RA and 16.7 (95%CI 16.4 to 16.9) per 100,000 PY for seronegative RA using Criteria A. A higher IR for seropositive RA than for seronegative RA was found regardless of the case criteria used. Figure 1 shows the temporal IRs of seropositive and seronegative RA.Regardless of case criteria used, the PP increased from 2000 to 2018 for both seropositive and seronegative RA, and the estimates were higher for seropositive RA than for seronegative RA (Table 1).Table 1.Point prevalence of rheumatoid arthritis in Denmark in year 2000, 2009, 2011 and 2018 using four different case definitions2000200920112018SeropositiveSeronegativeSeropositiveSeronegativeSeropositiveSeronegativeSeropositiveSeronegativeCriteria AN3029274174747127871281211243711662Population3964040416629842028914269677PP, % (95%CI)0.08 (0.08 to 0.08)0.07 (0.07 to 0.07)0.18 (0.18 to 0.19)0.17 (0.17 to 0.18)0.21 (0.20 to 0.21)0.19 (0.19 to 0.20)0.27 (0.27 to 0.28)0.26 (0.25 to 0.26)Criteria BN7507489311565903312710100111633413340PP, % (95%CI)0.20 (0.19 to 0.20)0.13 (0.12 to 0.13)0.28 (0.28 to 0.29)0.22 (0.21 to 0.22)0.30 (0.30 to 0.31)0.24 (0.23 to 0.24)0.36 (0.35 to 0.36)0.29 (0.29 to 0.30)Criteria CN6701457011174912512417101491588113712PP, % (95%CI)0.18 (0.17 to 0.18)0.12 (0.12 to 0.12)0.27 (0.27 to 0.28)0.22 (0.22 to 0.23)0.29 (0.29 to 0.30)0.24 (0.24 to 0.25)0.35 (0.34 to 0.35)0.30 (0.30 to 0.31)Criteria DN272423906612598476956759108309452PP, % (95%CI)0.07 (0.07 to 0.07)0.06 (0.06 to 0.07)0.16 (0.16 to 0.16)0.15 (0.14 to 0.15)0.18 (0.18 to 0.19)0.16 (0.16 to 0.17)0.24 (0.23 to 0.24)0.21 (0.20 to 0.21)PP = Point prevalenceConclusion:In Denmark, the IR and PP estimates were higher for seropositive compared to seronegative RA during the study period. However, when applying stricter case criteria for RA (Criteria A and D) the differences in IR and PP estimates were smaller, than when using less strict criteria (Criteria B and C). The findings of such small differences between seropositive and seronegative IRs warrant further investigation.