ROC analysis: ASDAS cut-offs for disease activity states and improvement scores according to several external criteria and according to three different methods of ‘optimal’ cut-off determination
| ASDAS cut-offs and external criteria | n (P+N) | 90% SP (SE/SP) | Youden (SE/SP) | (0,1) (SE/SP) | AUC (95% CI) |
|---|---|---|---|---|---|
| Cut-off between ‘inactive disease’ and ‘moderate disease activity’: | |||||
| ASAS partial remission | 336 (74+262) | <1.29 (64.9/90.1) | <1.60 (90.5/81.3) | <1.54 (89.2/82.4) | 0.91 (0.88 to 0.94) |
| Patient global <1 | 336 (77+259) | <1.35 (75.3/90.0) | <1.52 (87.0/84.1) | <1.52 (87.0/84.2) | 0.91 (0.88 to 0.94) |
| Physician global <1 | 331 (113+218) | <1.29 (44.2/89.9) | <1.95 (77.0/71.1) | <1.95 (77.0/71.1) | 0.79 (0.74 to 0.84) |
| Cut-off between ‘moderate’ and ‘high disease activity’: | |||||
| Patient global <3 | 336 (179+157) | <2.08 (79.3/89.8) | <2.46 (93.3/77.7) | <2.36 (89.9/80.9) | 0.94 (0.92 to 0.96) |
| Physician global <3 | 331 (258+73) | <2.14 (59.7/90.4) | <2.58 (75.2/80.8) | <2.58 (75.2/80.8) | 0.84 (0.79 to 0.89) |
| BASDAI <3 | 337 (154+183) | <1.94 (86.4/90.1) | <1.83 (85.1/92.3) | <2.05 (88.3/88.5) | 0.94 (0.92 to 0.97) |
| BASDAI <3.5 | 336 (181+155) | <2.17 (85.1/89.7) | <2.14 (83.4/91.6) | <2.17 (85.1/89.7) | 0.95 (0.92 to 0.97) |
| BASDAI <4 | 336 (202+134) | <2.24 (82.7/90.3) | <2.15 (79.7/94.8) | <2.34 (86.1/88.1) | 0.94 (0.92 to 0.97) |
| Cut-off between ‘high’ and ‘very high disease activity’: | |||||
| Patient global >6 | 477 (220+257) | >3.75 (61.4/89.9) | >3.58 (71.8/84.4) | >3.53 (73.6/82.5) | 0.86 (0.83 to 0.89) |
| Physician global >6 | 467 (55+412) | >4.62 (30.9/90.1) | >3.33 (87.3/52.4) | >3.50 (80.0/60.0) | 0.74 (0.67 to 0.81) |
| Cut-off for ‘clinically important improvement’: | |||||
| Better or much better* | 295 (209+86) | ≥1.12 (63.6/89.5) | ≥1.12 (63.6/89.5) | ≥0.68 (76.1/76.7) | 0.84 (0.79 to 0.88) |
| Cut-off for ‘major improvement’: | |||||
| Much better* | 295 (91+204) | ≥2.01 (56.0/90.2) | ≥1.32 (83.5/75.0) | ≥1.32 (83.5/75.0) | 0.85 (0.80 to 0.90) |
ASAS partial remission criteria are fulfilled if the value of the following four domains is below 2 (range 0–10): spinal pain, physical function measured by the BASFI, patient global assessment and inflammation measured as the mean of the last two BASDAI questions (severity and duration of morning stiffness).
↵* External criterion based on a unique NOR-DMARD question, in which patients rated the perceived change in their health status since the start of treatment on a five-point Likert-type scale (much better, better, unchanged, worse, much worse). The chosen cut-offs are highlighted in bold. Range of BASDAI and patient and physician global assessment is 0–10.
(0,1), cut-off according to the closest point to (0,1) criterion; 90% SP, cut-off according to the 90% specificity criterion; ASAS, Assessment of SpondyloArthritis international Society; ASDAS, Ankylosing Spondylitis Disease Activity Score; AUC, area under the curve; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; P+N, number of positive+negative results according to the external criterion; ROC, receiver operating characteristic; SE, sensitivity; SP, specificity; Youden, cut-off according to the Youden index criterion.