An external validation study reporting poor correlation between the claims-based index for rheumatoid arthritis severity and the disease activity score

Table 2 Adjusted correlations between additional claims-based variables related to rheumatoid arthritis severity and DAS28-CRP

Variable	Partial R ²
Original variables included in the algorithm to calculate CIRAS^a
Age	0.001
Gender	0.001
Inflammatory marker tests ordered	0.004
Rehabilitation visits (physical or occupational therapy visits)	0.0001
Rheumatoid factor test ordered	0.003
Platelet counts ordered	0.03
Number of chemistry panels ordered	0.001
Number of rheumatologist visits	0.004
Additional medical claims-based variables
Rheumatoid lung involvement	0.005
Hand surgery	0.006
Tuberculin test ordered	0.05
Anti-CCP test ordered	0.005
Additional pharmacy claims-based variables
Steroid use	0.004
Opioid use	0.05
NSAID use	0.0003
Number of non-biologic DMARDs used	0.03
Biologic DMARD use	0.05
Model R²	0.23

Data are from the Brigham and Women’s Hospital Rheumatoid Arthritis Sequential Study linked with Medicare claims (2006 to 2010). ^aA subsample of patients with pharmacy claims available (119 out of 315) was used to calculate these R² values. In this subsample, none of the patients had a Felty’s syndrome diagnosis. Therefore, that variable is not reported in this table. All of the variables were measured in the period of 365 days immediately prior to the DAS28-CRP (disease activity score in 28 joints calculated by using C-reactive protein) measurement date. CIRAS, claims-based index for rheumatoid arthritis severity; CCP, cyclic citrullinated peptide; DMARD, disease-modifying anti-rheumatic drug; NSAID, non-steroidal anti-inflammatory drug.

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