To determine the contribution of fibromyalgia (FM) to the subjective components 
of the Disease Activity Score 28-joints (DAS28) in patients with rheumatoid 
arthritis (RA), and to analyse the discriminatory performance of the derived 
DAS28 patient-reported components (DAS28-P) to identify patients with 
fibromyalgic RA. Consecutive RA patients underwent clinical and clinimetric 
assessment. The DAS28-P index was derived from the components of the DAS28 
scores by rearranging the DAS28-ESR formula. Patients were distinguished by the 
presence of FM. Student parametric t tests or Mann-Whitney non-parametric U 
tests were used to determine any between-group differences. Receiver operating 
characteristic (ROC) curve analysis was used to test the ability of the DAS28-P 
index to distinguish patients with RA and those with fibromyalgic RA. The study 
involved 292 RA patients (80.5% females, mean age 63 years) with a mean disease 
duration of 11.6 ± 8.5 years. Forty-three patients (14.7%) had concomitant FM, 
and significantly higher tender joint count (p < 0.001), pain numerical rating 
scale, global health status (p = 0.007), and DAS28 scores (p = 0.006) than those 
without FM. The DAS28-P values were also significantly higher in the patients 
with FM (0.68 ± 0.09 vs 0.58 ± 0.06; p < 0.001). The discriminatory power of the 
DAS28-P was very good (area under the ROC of 0.858, optimal cut-off value of 
0.631). The presence of FM strongly influences the DAS28 results. The assessment 
of patient-reported components to the DAS28 through the DAS28-P can be a useful 
way to identify patients with fibromyalgic RA.