Background/Purpose:

In some countries reimbursement criteria require a DAS28 score of >5.1 for initiating anti-TNF therapy in patients with rheumatoid arthritis. DAS28 score can be calculated based on C-reactive protein (CRP) levels (DAS28-CRP) or erythrocyte sedimentation rate (DAS28-ESR). The results of a recent mini-survey suggest that Turkish rheumatologists use DAS28-CRP more frequent. The aim of this study was to assess the agreement between the ESR and CRP based DAS28 scores in Turkish patients with RA.

Methods:

84 RA patients from one center with full data for both DAS28-ESR and DAS28-CRP were identified in our biological therapy database (TURKBIO). We compared their DAS28-CRP and DAS-ESR scores obtained from baseline and following visits.  Mean DAS28-ESR and DAS28-CRP values were compared by Spearman correlation and linear regression analysis. Bland-Altman analysis and kappa statistics were used to assess the agreement between the two DAS definitions in the whole group as well as in different gender and age groups.

Results:

Of the 84 patients 71 were females (85%) with a mean age (±SD) of 52.5 (± 14.2).   Disease duration was 10.5 years (±6.2) RF and CCP positivity was 58 % and 63%. DAS28-CRP and DAS28-ESR scores were available for 364visits. Mean DAS28-CRP and DAS-ESR values were 3.3 (±1.4) and 4.0 (±1.4)showing a strong correlation with each other [(Spearman correlation coefficient: 0.947, p<0.001) and linear regression analysis (R²=0.909, p<0.001)]. The agreement between the two DAS versions was good for both genders and all age groups with weighted kappa values ranging from 0.695  to 0.809  The number of visits with high disease activity based on DAS28-ESR was greater than that based on DAS28-CRP (p=0.08). 47 (49%) visits with moderate disease activity according to DAS28-CRP were classified as high according to DAS28-ESR (Table1). Bland-Altman plot analysis showed a mean difference (95% CI) of 0.69 (0.63 - 0.75) between the two methods (DAS28-ESR – DAS28-CRP), which was quite consistent in different gender and age categories (Table 2)

Conclusion:

The results suggest that DAS28-CRP may underestimate disease activity in RA patients, as compared to DAS28-ESR for both genders and different age groups. A significant proportion of patients, who would not qualify for reimbursement of anti-TNF therapy according to DAS28-CRP would be classified as having high disease activity according to DAS28-ESR.

Table-1.Agreement between DAS28-ESR and DAS28-CRP on the classification of the patient visits into different categories of disease activity

		DAS 28 ESR
		≤3.2	3.21-5.10	≥5.11	Total
DAS 28 CRP	≤3.2	128	64	0	192
	3.21-5.10	0	74	47	121
	≥5.11	0	2	49	51
	Total	128	140	96	364

Table 2. Summary of Bland-Altman plot data for comparison of  DAS-ESR and  DAS-CRP in different gender and age categories

Patients  (# of patients, # of visits)	Mean difference (95% CI)	Lower Limit (95% CI)	Upper Limit (95% CI)
Females (n=71, n=308)	0.735 (0.688 -0.783)	0.097 (0.179-0.015)	1.569 (1.487-1.651)
Males (n=13, n=56)	0.471 (0.357-0.589)	0.377 (0.576-0.177)	1.324 (1.124-1.524)
≤40 years  old (n=17, n=65)	0.481 (0.377-0.588)	0.369 (0.533-0.184)	1.331 (1.147-1.516)
41-60 years old (n=42, n=182)	0.791 (0.667-0.795)	0.094 (0.200-0.011)	1.553 (1.447-1.659)
≥61 years old (n=25, n=117)	0.761 (0.683-0.840)	0.080 (0.215-0.054)	1.603 (1.468-1.738)
Overall (n= 84, n=364)	0.695 (0.650-0.740)	0.160 (0.237-0.083)	1.551 (1.473-1.628)

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/difference-between-the-two-versions-of-disease-activity-score-based-on-c-reactive-protein-and-erythrocyte-sedimentation-rate/