The influence of patient demographics on disease activity measurments in theumatoid arthritis

• Background: Several indexes have been constructed for the measurement of disease activity in rheumatoid arthritis (RA) patients, including the Disease Activity Score 28-joint count, which either includes the Erythrocyte Sedimentation Rate (DAS28ESR) or the C-reactive protein concentration (DAS28CRP), and the Clinical Disease Activity Index (CDAI). The categorization of the results of these three indexes into levels of disease activity (Remission, Low, Moderate and High) is used to assess patient outcomes, and to guide medical decisions regarding treatment. However, the different indexes can lead to somewhat different classification, and hence influence treatment decisions.1 Objectives: To investigate how DAS28ESR, DAS28CRP and CDAI indexes are associated to age and sex in RA patients. To investigate the agreement between indexes and between categories of disease activity levels.Methods: We identified a cohort of RA patients, registered in the Swedish Rheumatology Quality Register between January 1st2014 and December 31st2017. The indexes were obtained from the first visit at the time point of RA diagnosis, and at the visit registered at the start of a first ever biological treatment prescription. Linear models were used to investigate the correlation between the indexes, age and sex. The agreement between the indexes was explored with Bland-Altman plots. The agreement between disease activity levels was evaluated through kappa statistics.Results: Data were analyzed for 3855 RA patients (2576 women, mean age ±SD=60±15) at their first diagnosis visit and for 3062 RA patients (2313 women, mean age ±SD=57±14) at the start of their first biologic. Similar results for all subsequently described analyses were obtained at both time points. The correlation coefficient and 95% confidence interval (95%CI) between the indexes and age were 0.093 (0.063-0.124) for DAS28ESR and 0.055 (0.025-0.085) for DAS28CRP at the first visit, while CDAI was not correlated to age. There was no difference between men and women for CDAI and DAS28CRP, while DAS28ESR presented a mean difference of 0.1 unit between men and women. The agreement between categories of disease activity was moderate: at the RA diagnosis visit, the kappa statistics and 95% CI were: 0.63 (0.61-0.65) between DAS28ESR and DAS28CRP, 0.59 (0.57-0.61) between DAS28ESR and CDAI, and 0.55 (0.53-0.57) between DAS28CRP and CDAI. About 25% of the patients were classified differently. The Bland-Altman plot revealed that the difference between DAS28ESR and DAS28CRP depended on sex and slightly increased with age.Conclusion: Factors related to patient demographics might influence the results of disease activity indexes. This has a potential to affect clinical decisions, as the definition into disease activity categories can differ depending on the score used. This suggests the need to consider sex and age when defining such categories and interpreting results from these indexes.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Reumatologi och inflammation (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Rheumatology and Autoimmunity (hsv//eng)

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