Background: ASDAS value of ≥ 2.1 has been proposed as a threshold to define high disease activity and as a suitable cut-off for eligibility for anti-TNF therapy. However, using this criterion results in more patients being eligible for anti-TNF treatment (1), as compared to the BASDAI cut-off ≥ 4 which is an eligibility criterion for anti-TNF therapy in many countries. In Turkey a BASDAI score ≥ 5 is required.

Objectives: To estimate the ASDAS-CRP threshold values corresponding to BASDAI scores of ≥4 and ≥5.

Methods: Data were obtained from the local clinical database which contains slightly over 500 AS patients. Patients with full data for ASDAS-CRP and BASDAI at baseline were included in this analysis. Mean ASDAS CRP and BASDAI values were compared by Spearman correlation. Receiver operating characteristic (ROC) curves was constructed to assess the cut-off points of ASDAS-CRP values that correspond to BASDAI scores of 4 and 5. Each cut-off point was calculated on the basis of the best trade-off values between sensitivity and specificity.

Results: 396 patients (291 M; 44 ±12.0) were identified with complete data at baseline for this analysis. Mean disease duration was 9.4 ± 8.2. Mean BASDAI, BASFI and BASMI scores were 3.6 ± 2.3, 2.9 ± 2.6, 3.9 ± 1.9, respectively. HLA B27 was positive in 65% of the tested patients. 83.7% of the patients were using NSAID and 20.7% of patients were using anti TNF agents. There was very good correlation between ASDAS CRP and BASDAI when tested by Spearman (p<0.001; r=0.9). Of the patients with ASDAS ≥ 2.1 (n=296), 43.5% had a BASDAI score <4 and 59.7% BASDAI <5 (Table). Agreement between ASDAS≥2.1 and BASDAI≥4 was found to be only fair (n=0.39). The best trade-off ASDAS-CRP value corresponding to BASDAIscores of 4 and 5 were 2.9 (80% sensitivity and 77% specificity; AUC: 0.88) and 3.0 (81% sensitivity and 74% specificity; AUC: 0.86), respectively.

Conclusions: The ASDAS value that corresponds to the recommended BASDAI cut-off ≥4 for initiation of anti-TNF therapy is higher than the recommended ASDAS threshold of ≥ 2.1. Most likely, BASDAI eligibility criterion will continue to be widely used for selecting AS patients for anti-TNF therapy, until the reimbursement regulations include an ASDAS based criterion.

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Disclosure of Interest: None Declared