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

Background: Few previous studies have investigated the incidence rate (IR) and point prevalence (PP) of seropositive seronegative rheumatoid arthritis (RA), further, estimates remain unknown in Danish population. Objectives: To investigate IR PP RA adult population from 1998 to 2018 using four register-based case definitions RA. Methods: Nationwide cohort study. Using administrative registers, patients with between end were identified. ICD-10 codes for identified National Patient Registry information on DMARD prescriptions obtained through Prescription ATC codes. The used 1 : Criteria A, first time M05/M06 diagnosis redemption a following year; B, two diagnoses within 90 days each other, originating department rheumatology or general internal medicine, where latest registered defined serologic status; C, recorded at any preceded followed by prescription one year, determined D, as but additional requirements that cases had no registration other selected inflammatory diseases. In calculation IRs total was reference standardisation. calculated years 2000, 2009, 2011 2018. Results: From overall 18.0 (95%CI 17.7 18.3) per 100,000 person (PY) 16.7 16.4 16.9) PY A. A higher than found regardless criteria used. Figure shows temporal Regardless used, increased 2000 both RA, (Table 1). Table 1. Point Denmark year different 2009 Seropositive Seronegative N 3029 2741 7474 7127 8712 8121 12437 11662 Population 3964040 4166298 4202891 4269677 PP, % ) 0.08 (0.08 0.08) 0.07 (0.07 0.07) 0.18 (0.18 0.19) 0.17 (0.17 0.18) 0.21 (0.20 0.21) 0.19 (0.19 0.20) 0.27 (0.27 0.28) 0.26 (0.25 0.26) B 7507 4893 11565 9033 12710 10011 16334 13340 0.20 0.13 (0.12 0.13) 0.28 (0.28 0.29) 0.22 (0.21 0.22) 0.30 (0.30 0.31) 0.24 (0.23 0.24) 0.36 (0.35 0.36) 0.29 (0.29 0.30) C 6701 4570 11174 9125 12417 10149 15881 13712 0.12 0.12) (0.22 0.23) (0.24 0.25) 0.35 (0.34 0.35) D 2724 2390 6612 5984 7695 6759 10830 9452 0.06 (0.06 0.16 (0.16 0.16) 0.15 (0.14 0.15) 0.17) = Conclusion: Denmark, compared during study period. However, when applying stricter (Criteria D) differences smaller, less strict C). findings such small warrant further investigation. References: [1]Soussi BG et al. Incidence Denmark: nationwide based investigating effect [abstract]. Ann Rheum Dis. 2020;79(supplement 1):46 Acknowledgements: authors will like thank Rheumatism Association supporting this work. Disclosure Interests: Bolette Gylden Soussi: None declared, René Lindholm Cordtz: Salome Kristensen: Christian Sørensen Bork: Jeppe Christensen: Erik Berg Schmidt: Daniel Prieto-Alhambra Grant/research support from: Grants AMGEN, UCB Biopharma Les Laboratoires Servier; Janssen, behalf IMI-funded EHDEN EMIF consortiums, Synapse Management Partners supported training programmes organised DPA’s open external participants, Lene Dreyer BMS, Galderma Eli Lilly.