This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
Two scores for axial spondyloarthritis
Axial spondyloarthritis, which includes ankylosing spondylitis, causes inflammatory back pain, stiffness and fatigue. Two scores are used to follow its activity:
- the BASDAI (Bath Ankylosing Spondylitis Disease Activity Index), a six-question patient questionnaire;
- the ASDAS (Ankylosing Spondylitis Disease Activity Score), which combines patient answers with CRP.
The BASDAI
The patient rates each question from 0 to 10 for the past week:
- Fatigue
- Neck, back or hip pain
- Pain or swelling in other joints
- Discomfort from areas tender to touch or pressure (entheses)
- Severity of morning stiffness
- Duration of morning stiffness (0 = none, 10 = 2 hours or more)
BASDAI = (Q1 + Q2 + Q3 + Q4 + (Q5 + Q6) ÷ 2) ÷ 5
A BASDAI of 4 or more is the classic definition of active disease and has long been used to decide whether to start or change biologic treatment.
The ASDAS-CRP
ASDAS = 0.12 × back pain + 0.06 × duration of morning stiffness + 0.11 × patient global + 0.07 × peripheral pain or swelling + 0.58 × ln(CRP + 1)
CRP is in mg/L; values under 2 mg/L are replaced by 2. The calculator reuses BASDAI questions 2, 6 and 3 for back pain, stiffness duration and peripheral symptoms.
| ASDAS | Disease activity |
|---|---|
| under 1.3 | Inactive |
| 1.3 to 2.0 | Low |
| 2.1 to 3.5 | High |
| above 3.5 | Very high |
A fall of 1.1 or more is a clinically important improvement, and 2.0 or more a major improvement.
Example
Answers of 5, 6, 4, 3, 6 and 5 give a BASDAI of (5 + 6 + 4 + 3 + 5.5) ÷ 5 = 4.7: active disease. With a patient global of 5 and a CRP of 8 mg/L, the ASDAS is 3.12: high activity.
Which one to use?
International recommendations (ASAS-EULAR) now prefer the ASDAS, because it includes an objective inflammation marker and has validated cut-offs for activity and response. The BASDAI remains widely used and useful when no recent CRP is available.