Background The nationwide DANBIO registry includes data on patients with rheumatoid arthritis (RA) and their treatment with biological disease modifying anti-rheumatic drugs (bDMARD), functional status as well as time for onset of symptoms, and establishment of diagnosis.
Objectives To investigate whether delay of diagnosis predicts deterioration in functional status in RA patients in bDMARD treatment.
Methods The analysis was based on longitudinal data on 3,199 RA-patients who received bDMARD treatment and were entered into DANBIO between 2001 and 2011. Diagnostic delay (time from symptom onset to RA diagnosis) was categorized into three groups: <4 months, 4-12 months, and >12 months. Functional status was assessed by the Health Assessment Questionnaire (HAQ). The patients had a total of 36,316 complete visits in DANBIO while on bDMARD therapy. Predictions of HAQ were analyzed in mixed linear regression models with a random intra-individual variation.
Results Women accounted for 74% of the study population. On average, patients were aged 54.1 (SD 14.0) years at diagnosis, and 56.8 (SD12.7) years at first visit. The average treatment time on bDMARD was 24.5 (SD 24.7) months and diagnostic delay was on average 22.5 (SD 44.5) months. Diagnostic delay above 12 months predicted higher average HAQ (0.98 SE 0.02) compared with HAQ in RA-patients with delay time of less than 4 months (0.92 SE 0.02) and 4-12 months (0.91 SE 0.02). This association was statistically significant (both p<0.05) after adjustment for age at diagnosis, age at first visit, sex, comorbidities, and geographical region. The length of treatment time moderated the association significantly, so that a longer treatment length was associated with lower average HAQ: p<0.05 between HAQ of patients with delay time of less than 4 months and above 12 months. For 40-49 year-olds, the expected HAQ was 0.95 (SE 0.02) with diagnostic delay of less than 4 months, 0.95 (SE 0.02) with delay time of 4- 12 months, and 1.02 (SE 0.02) with diagnostic delay more than 12 months. Similarly, for 60-69 year-olds, the average HAQ was 0.81 (SE 0.03) with delays less than 4 months, 0.81 (SE 0.02) with delays of 4-12 months, and 0.88 (SE 0.02) with diagnostic delay time of above 12 months.
Conclusions Delay of diagnosis of more than 12 months predicted poorer functional health status in RA-patients during bDMARD treatment.
Acknowledgements The study was partly funded by the Danish Rheumatism Association by an unrestricted grant.
Disclosure of Interest : None declared