The BASDAI Score Explained: What Your Number Means for AS
If you have ankylosing spondylitis (AS), sooner or later a rheumatologist will ask you to fill in the BASDAI. It's short, it looks simple, and the number it produces can decide whether you're offered a biologic. Here's what it measures, how the score works, and what the numbers that matter actually mean.
What the BASDAI is
The Bath Ankylosing Spondylitis Disease Activity Index was developed in 1994 by Garrett and colleagues at the Royal National Hospital for Rheumatic Diseases in Bath. It's a self-report questionnaire: six questions about the past week, each answered on a scale from 0 (none) to 10 (very severe).
- Fatigue: how tired you've felt overall.
- Spinal pain: pain in your neck, back or hips.
- Joint pain and swelling: in joints other than the neck, back or hips.
- Tender spots: discomfort from areas that hurt when touched or pressed (often where tendons and ligaments attach to bone).
- Morning stiffness, how bad: its severity from when you wake up.
- Morning stiffness, how long: from 0 to 2 hours or more.
How it's scored
The two morning stiffness questions are averaged first, so stiffness counts once rather than twice. Then that average is added to the other four answers and the total is divided by five:
BASDAI = (Q1 + Q2 + Q3 + Q4 + (Q5 + Q6) / 2) / 5
The result runs from 0 to 10. Higher means more active disease.
Why 4 is the number everyone talks about
A BASDAI of 4 or more is widely used as the line for active disease. In the UK, NICE guidance uses it to decide who can start a biologic or JAK inhibitor: typically a BASDAI of at least 4 together with a spinal pain score of at least 4, on two occasions at least 12 weeks apart, despite standard treatment such as anti-inflammatories. Other countries and insurers use similar thresholds.
The same idea works in reverse once treatment starts. A drop of at least 2 points, or to half of your starting score, is commonly used as the sign that a treatment is working, which is why your rheumatologist may repeat it a few months in.
What it doesn't tell you
The BASDAI is entirely about how you feel, which is its strength and its weakness. It doesn't include blood tests or scans, so many rheumatologists also use the ASDAS, which combines some of the same questions with an inflammation blood test (CRP). And because it covers only the past week, a single bad or good week can make it misleading on its own.
Getting the most out of it
- Track it between appointments. A score taken monthly shows a trend. One score taken on the day of your appointment shows a single week.
- Note what was going on. A flare, an infection or a stressful week all push the number up. A note next to the score helps your rheumatologist read it.
- Bring the history. Two scores above 4, twelve weeks apart, is exactly what the biologic criteria ask for. Having them written down saves an extra wait.
Track your BASDAI between appointments
Spondy includes the BASDAI, reminds you when it's time to retake it, and keeps your scores next to your daily logs, flares and medications, ready to share with your rheumatologist.
This article is for general information and isn't a substitute for medical advice. Talk to a doctor about your own symptoms, tests and treatment.